Hello everyone! Per
The question being asked was:
If a player plans to stick to the low- and mid-tiers (2-7), what are the best lines in the game for them?
This is a common scenario for F2P players, because at tier 8 tanks are more expensive to play, and at tiers 9+ it's hard to break even with credits. I recommend this for new players – high tiers are very competitive, and it's better to have fun at tier 5 than burn out because you hate / can't afford tier 10.
Below are my opinions, grouped into "Best", "Good", "Honorable Mentions", "Save for Later", and "The Rest". Below that is some info on which research paths are the best, and which skippable tanks are worth playing (basically just the KV-2). I won't include SPGs, as through the mid tiers they're all pretty similar, and to be honest low-tier SPGs are not fun to play.
When I started, I picked what tank to grind for next by which one I found most difficult to fight against. For example, as a noob I couldn't pen the M4A3E2, but once I got one, people started penning me easily! This taught me where the weakspots are. Often, this was a great way to find a new favorite tank. Guides age as game balance changes, so even if the recommendations below get old, don't forget the above, tried-and-true method!
The best of the best, the lines all new players should be looking at.
American TDs (T25/2): lots of strong low- and mid-tier tanks. The T67 is a statpadder's dream and the Hellcat is still a blast to play. The only underwhelming tank is the T25/2 but even it is an alright MT/TD hybrid. Solid high tiers make this worth continuing when you're ready for it. Make your way up to the tier 7, keeping any tank that interests you along the way.
American TDs (T25 AT): called the "non-turreted" line, which is a bit of a misnomer because tiers 5-6 have turrets. A similar story to the other line, with strong showings up through tier 6. The tier 7 T25 AT isn't bad either, but it's nothing special. I'd put the Hellcat line above this one, but both are very solid. The top tiers are very good at what they do. At least play through tier 6, and do the tier 7 if it interests you.
American MTs: once you get past the most famous hurdle in the game, the M3 Lee, this line delivers. The tier 5 M4A1 is one of the strongest and most well-rounded mediums of its tier, and the tier 7 T20 is arguably the best MT of its tier. Tier 6 is less exciting, but the M4A3E2 "Sherman Jumbo" has more armor than some heavies. The top tiers are excellent, especially tiers 9-10. Worth grinding all the way to tier 7, and keeping the tier 5.
British MTs: this line is very commonly recommended, but there are exactly three vehicles that make it worthwhile: the tier 2 Cruiser III, tier 3 Cruiser IV, and tier 6 Cromwell. Tiers 4 and 5 are not great but are at least playable, and the tier 7 Comet has quite a bit of potential if you can work around its poor penetration. All new players should try out these low-tier Cruisers, and the Cromwell is a staple recommendation. The tiers 8-10 are generally worth the grind as well. Get the tier 6, and keep the low tiers that you enjoyed.
British TDs (Challenger): an uncommon suggestion, but it is one of the better lines. You can access this via the "lend-lease" medium branch or the "Valentine" branch. I'd recommend the latter: the tier 2 is meh, but the tier 3 Cruiser II has a hilarious howitzer that obliterates whatever it hits. The tier 4 is really not that good, and few players like the tier 5, but the tier 6 Achilles is truly a hidden gem, thanks to its phenomenal gun and rather functional platform. If you go lend-lease, the low tiers are okay, you get to suffer through another M3 variant, but you're rewarded with the tier 5 Sherman III that's much more playable than the Archer. The tier 6 Firefly is good, but I think the Achilles is better. The tier 7 Challenger is very fun, especially with the top gun. The top tiers are unusual but eventually worth getting. Pick the Cruiser I branch, grind to tier 7 and keep at least the tier 3.
French LTs (tracked): the low tiers are LTs only in name, with the tier 4 having significantly more armor than tier 4 heavy tanks. The line comes into its own at tiers 5+, starting with legendary AMX ELC bis. A shadow of its former self, but fun and capable nonetheless. The tier 6 is very deadly, and the tier 7 would feel better if the blatantly OP T71 DA didn't exist. Another line worth continuing, as it leads to three tier 10s. Grind it to at least tier 6, and keep the 5 if you enjoyed it.
German MTs (Panther): they barely make the cut, but I'll give them a pass. These are the only mid-tier medium tanks that feel "tough". They have tough armor, surprisingly good mobility for the weight, and accurate sniping guns that make for a weird but potentially fun combination. Easy enough to like but hard to love, it's a fine line to know when you can and can't rely on your armor. Besides the tier 4 D.W. 2, though, nothing in this line is awful, the Panther is historical, and who knows, you might be one of the lucky few to figure out this tank right away. The high tiers play a lot like the Panther, which is a good thing if you liked the Panther. At least finish the tier 6, and if by the end of the grind you aren't enjoying the playstyle, stop and revisit the line at a later time.
Russian HTs (IS): one of the most popular and most capable heavy tank lines in the game. The tier 2 is underwhelming, but I found the tier 3 T-46 to be a lot of fun. The tier 4 is pretty painful for new players, but at least it gets a good gun. Tier 5 is where the line takes off, starting with the best tier 5 HT in the game, the KV-1. Strong turret armor, thick side armor that's great for teaching you about sidescraping, and three solid gun options, you just can't go wrong with this one. You have to research a second tier 5, the KV-1S, which is about as good of a tank. The KV-1S focuses more on mobility, with noticeably thinner turret armor but similar hull armor in practice, and the 122mm is the preferred gun. The tier 6 KV-85 would be a great tank if it didn't have only 3 degrees of gun depression – this can be very painful to work around. The tier 7 IS is worth the effort, as it has nice mobility, unreliable yet bouncy armor, solid penetration, and a very impressive 390 damage per shot. My biggest complaint is the bad gun handling, but it's awesome. As with the Russian MTs, the real reason to play this line is for the high tiers, of which there are many good options. Grind it to tier 7, keep the KV-1 as well as any other tanks you enjoyed along the way.
Russian HTs (KV-3): the one line here that benefits most from your request to stop at tier 7. The IS line plays like the KV-1S, so logically this plays like the KV-1. It's slower, has better turret armor, and at least at tier 6 has a bigger gun. The tier 6 T-150 is arguably the best brawler of its tier, and the tier 7 KV-3 is not too far behind. If you're looking to the future, though, the tier 8 KV-4 is one of the most detested vehicles in the game, and the tier 10 IS-4 is no different. Sandwiched between these two turds is the truly amazing tier 9 ST-I, which is arguably the best brawler of its tier. Grind it to tier 6 and maybe tier 7.
Russian TDs (SU-152): one of the best TD lines in the game, this line is defined by reasonable mobility, good concealment values, and terrifying firepower. Especially as a new player, you'll enjoy the excellent tier 3 and 4 tanks this line has to offer. The tier 6 SU-100 is the first indication that the line is truly special, a feeling only reinforced by the tier 7 SU-152. These tanks are defined by their ability to do monstrous amounts of damage. The high tiers are mixed – the tier 8 is quite possibly the scariest tier 8 TD in the entire game, and the tier 9 is a solid performer, but the tier 10 lags a bit. Still, you won't regret grinding this line. Get to tier 7 and keep any and all tanks you enjoyed along the way.
Russian TDs (SU-100M1): only different from the above by the tier 7 tank – the high tiers differentiate these two lines. The SU-152 line is for sniping, and this line is for brawling. The SU-100M1 has phenomenally thick armor, better than most higher-tier heavy tanks (no I am not kidding), has great camo, and very good straight-line speed. However, the gun is subpar, it turns slowly, and if the enemy can pen you, you'll find the hitpoint pool lacking. The high tiers are good, with 8 and 9 being pretty good and 10 being very strong. Get to tier 7.
Solid lines that didn't make the cut but are still worthwhile.
British TDs (AT 7): the low tiers are all over the place but the line takes shape at tier 5 with the AT 2. From here onwards, this line is very slow, very well armored, and often well-armed. They have weakspots that are mostly for decoration, as they are about as thick as your main armor. That said, don't stray too far from cover or fire support, lest a light tank do inappropriate things to your behind. Many people find these too painful to play due to their sluggish nature; others adore them for their ability to shrug off inordinate amounts of ordnance. Above-average hitpoint pools improve their survivability further. The line is quite consistent, and even if the tier 10 is a bit different the tier 9 is still worth playing. Get the tier 5, but only keep playing if you enjoy that playstyle.
Chinese LTs: the low tiers are often forgotten but are truly excellent. The tier 2 is really potent, tier 3 is well-rounded, and tier 4 is arguably the best tier 4 scout tank that isn't named "Luchs". The light tanks themselves are worth a mention because of their above-average firepower – they're one of the only LT lines that can spot and do its own damage. This is appealing for new players who are looking to dip their toes in the world of LTs. The high tiers are nothing special, but with your low-tier focus this line cannot be ignored. Worth going all the way to tier 7, keeping select low-tiers as you go.
German TDs (Jagdpanther): a solid line with a couple really good low-tiers. The Hetzer is the stuff of legend, a low tier tank that every player should have, and the line from that point on is pretty solid. It struggles to choose between brawling or sniping at times, but it can do both pretty well. None of the tanks past tier 4 are incredible, but none of them are bad either. The high tiers get really heavy really fast but the playstyle stays consistent through tier 7. The top tiers are not the best, but they have their appeal. Worth going all the way to tier 7.
German TDs (Sturer Emil): a less common recommendation, but these tanks are really quite decent. The tier 4 is quite fun, tier 5 has a punchy gun if you can hide its massive bulk, and the tier 6 is arguably the best sniper of its tier. The tier 7 is a bit of an oddball, excruciatingly painful when stock and downright strange when elite, but if you can combine its eclectic strengths it makes for a formidable tank. The main reason to play this line is for the tiers 8-9 vehicles, as the tier 10 is widely disliked. Worth going all the way to tier 7, but don't feel bad if you dislike a couple of vehicles along the way.
Italian MTs: one of the newer lines, but still pretty friendly to newer players. Their above-average armor is more forgiving of mistakes, and though players are sharply divided on whether the tier 6 or 7 is best, you'll really enjoy at least one of them. The tier 5 is merely alright, but that's not too great a sin to commit. This line is really worth playing for the high-tiers (which are "save it for later"), but even if you stop at tier 7 they're worth a look. When you're ready, you must try out the tier 8. Worth grinding to tier 7.
Japanese HTs: the low tiers suck, that's all there is to it, but once you get to tier 5 you start getting functional armor and the line really comes into form. The only real problem I have with this line is its armor profile: it's thick and flat with few weakspots, so as a new player who makes many little mistakes it's very forgiving, but it also won't teach you too many good habits. You'll undoubtedly get dicked by O-Is many times, so it's worth getting the tank just to be the one doing the dicking. The high tiers are not the best, but up through tier 7 they're pretty good. Worth grinding to tier 6, but 7 and up are optional.
Russian MTs (A-44): this only differs from the below line by two tanks, so I'll refer you to it for tiers 2-5. The tier 6 is a hidden gem at tier 6, best compared to the Cromwell. When wielding the 57mm, it has noticeably lower alpha, gun depression, and top speed than its British counterpart, but in exchange gets amazing gun handling for its tier. The A-43 can in fact hit the broad side of a barn while moving, something the Crommy struggles with. The A-44 is one of the weirdest tanks in the game, with a hard-hitting, inaccurate gun that is best for brawling, thick armor, a tiny rear turret, and good mobility. The tier 8 is incredible in the right hands, and the rest of the high tiers are good if you are skillful enough to use them. Grind it to tier 6, and save the high tiers until you're ready.
Russian MTs (T-43): one of the most popular medium lines in the game. Two low-tier paths are available, of which the BT-line is probably preferred. The tier 5 T-34, a tank of legend, has the performance to match its real-world reputation, thanks to an excellent gun and above-average hull armor. The tier 6 may be nudged out of the top spot in its tier but it's a solid vehicle overall. The only "meh" tank is the tier 7, and it's still alright. The real appeal of this line is tiers 8-10, which contain some of the strongest vehicles in the game. If you're capping yourself to tier 7, though, this line is less exciting. Grind it to tier 6, and consider making this your first tier 8.
Swedish TDs: fast, sneaky, and with good gun depression, these TDs are known for their incredible camo values. The low tiers are pretty standard, but the tier 5 Ikv 103 has a very unusual gun that makes it better at hit-and-run tactics instead of sniping. The next two vehicles are more traditionally armed: the tier 6 is rather good, but the tier 7 is underwhelming. You have to understand vision mechanics, particularly how to shoot through opaque bushes, to make the most of this line, but the high base camo makes the tier 6 a pretty good place to start. The high tiers are absolutely fantastic. Worth grinding to tier 6, and keep the tier 5 if you liked it, just know that the 7 is only worth grinding if you're going for tiers 8+. Note that the tier 8+ TDs have fantastic silver pen that make them profitable for free-to-play players; however, not everyone enjoys them.
Lines that are either less special, or only have a handful of strong vehicles.
American LTs (T71 DA): one of those lines that's mostly worth getting for the tier 7. The low tiers are mixed, with an incredible tier 2, mediocre tier 3, and awful tier 5. The tier 5 M7 is pretty good and the tier 6 T21 is way better than people give it credit for, but the star of the show is the tier 7 T71 DA. It's fast, it's accurate, and it has a monstrous 900dmg clip potential that devastates whoever is on the receiving end. Most big-clip autoloaders make some sacrifice to get that damage potential, but this tank doesn't. From there, the tier 8 is widely disliked, the tier 9 has its fans and detractors, and the tier 10 is quite good if unusual. Get the tier 2, and at some point get the tier 7.
American HTs: there's only one tank in your tier limit that is worth playing, but it is definitely worth the grind: the T29. The terror of tier 7, it dominates ridgelines and is a great vehicle for teaching new players how to go hulldown. Sadly, this is the last great tank in the line, though I'll defend the tier 9 M103 to the bitter end. It's a lot of effort for just one tier 7 tank, but it's worth it.
Czech MTs: another line with one tank that makes it worth it, the tier 6 Škoda T 25 is incredibly powerful and a ton of fun to play. It is not nearly as popular as it should be. This line is otherwise mostly average, only getting interesting again at tier 9-10. Stop at the tier 6 until you intend to go to the high tiers.
German LTs: the tier 3 Pz I C, tier 3 Pz II G, tier 4 Luchs, and to a lesser extent the tier 5 Leopard, are your sole reasons to play this line, but goddamn are they good reasons. They are a ton of fun for new players in the low tiers, and I strongly recommend getting them. However, the rest of the line isn't really worth it, and it only gets worse the higher you go. Don't go past tier 5 – the mid tiers aren't bad per se, they just aren't worthwhile.
German MTs (VK 30.02 D): often overlooked, these vehicles are a lot better than people give them credit for. They're well rounded, with great mobility, good guns, and pretty okay armor to boot. They don't manage to stand out a lot, not to mention the high tiers in that line were only very recently buffed, but they're worth your time. I consider the tier 5 Pz III/IV to be a bit of a hidden gem. The top tiers are worthwhile. At least get the tier 5, but only get the tier 7 if you enjoy the tier 6.
German HTs (Tiger I): the very first line most new players go down, mostly for name recognition. The tier 5s are good, but the tier 6 is just alright. The tier 7 Tiger itself is quite good, but for none of the reasons you'd think: it's quite fragile, but it has a massive health pool and a high DPM gun that chews through opponents faster than they can chew through it. You can reach this through three different branches, and I recommend the ones that take you through the Pz IV H. Do not be too eager for the Tiger II, and the top tiers as a whole rank in the middle in terms of desirability. Worth getting the tier 7, but this line's priority should not be in your top 5.
German HTs (Tiger P): the tier 5 is solid and the tier 6 is frankly amazing, but the tier 7 heavy is quite unfortunate, as its gun has an unenviable combination of low damage, low DPM, and bad gun handling. The only reason to play this tank is for the two tier 8 HTs it leads into. Yes, it leads to the Ferdinand as well, but trust me when I say you'd be better off playing an entire German TD line than playing the Tiger P any longer. The Maus line is worth it, the Pz. VII line less so, but do your research before committing to either. Get the tier 6, but don't bother with the tier 7 until you're ready to get the tier 8s.
Russian LTs: the tier 2 and 3 tanks are wicked fast and worth getting just for fun, but the mid-tiers are less exciting. The only vehicle here worth mentioning is the LTG, which is arguably the best non-autoloading tier 7 LT, thanks to its solid firepower, excellent mobility, and very low profile. This line is mostly worth playing to get the tier 10 LT, which is still considered to be the best tracked tier 10 LT in the game. Get the tier 2 and 3, and eventually the tier 7.
Swedish MTs: they are fragile, relatively mobile medium tanks with good guns and amazing gun depression. The low tiers are nothing special, but the tier 4 Lago is rather decent. The tier 5 Strv m/42 is one of the few "average" tier 5 MTs with a standout feature, high alpha damage. The tier 6 Strv 74 is exceptionally comfortable, with 15 degrees of gun depression, great gun handling, and a solid all-round gun, but I found it kinda boring. The tier 7 Leo can be normal or very not-normal, depending on which gun you pick, but at least it's unique. They don't quite make the cut for low- and mid-tier performance, but both high-tier lines are worthwhile. Get the tier 7, but as a whole this line has lower priority.
Save For Later
Lines with a lot of potential but for one reason or another should be saved for later.
American LTs (T71 CMCD): a solid light line, with an especially strong showing at tier 2. From here, it's not as great: the tier 3 is fine, but the tier 4 is garbage. The tier 5 was once my favorite tank in the game, but the final nerf killed it for me; that said, it's still okay. The tier 6 and 7 are pretty good, though the latter fails to stand out. The high tiers are pretty decent. It's by no means a bad line, and it's definitely the most "comfortable" LT line, but I consider it of average priority. Get the tier 2 and maybe the tier 6, from there it's up to you.
British HTs: no other line in the game is this inconsistent in the low tiers. The tier 2 is fine, but I found the tier 3 intolerable. It's worth it to get the legendary tier 4 tank, the Matilda, whose thick armor and reliable gun are very fun. The issue is with the rest of the line: the tier 5 is fine, no one's favorite but perfectly adequate, but it goes downhill from there. The tier 6 Churchill VII is agonizing, my personal least favorite tank in the game, due to its numerous weaknesses and very few good traits. The tier 7 is often equally disliked, but its solid gun depression and amazing turret armor (second only to the T29) makes it quite playable and borderline fun. That said, the only reason people suffer through this line is for the tiers 8-10, which are all incredibly strong. Get the tier 4, but don't go past that until you want the tier 8 and have a lot of vodka to drown your sorrows.
Chinese HTs: this has the same low-tiers as the Chinese LT line. The high tiers are some of the strongest and most fun high-tier heavy tanks in the game; however, this line only takes off at tier 9. The tier 6 is mediocre but the tier 7 is good enough to earn the line a place on this list. The tier 8 is okay at best, but tiers 9 and 10 will definitely be worth some attention, when you're ready to start playing those tiers. Get the tier 7, but it's a very low priority until you're ready to push for tiers 9-10.
French LTs (wheeled): the low tiers are pretty balanced and don't play too differently from regular LTs. However, they are much harder to drive because of their wheeled suspension and the game's wonky physics. That said, if you can get the hang of it they can be a blast. The high tiers get wicked fast. Get the tier 6 just for fun, but don't bother with the tier 7 until you're ready to get the tier 8.
French HTs (autoloaders): the AMX 50 B line is very capable, and does play like a standard HT line up through tier 6, but tiers 7-10 are very unusual and require a fair bit of player skill. The tiers 2-3 are okay, and the tier 4 is a bit of a turd but at least it's a short grind. The tier 5 BDR G1 B is a bit of a hidden gem , with workable armor and a punchy gun, and the tier 6 ARL 44 has some potent guns. The tier 7 AMX M4 45 is a puzzle to be solved, and the tier 8 AMX 50 100 is a beast to be tamed. Ultimately worth the grind, but only when you're ready. Get to tier 5 or 6 if you want, but postpone the line as a whole until you're ready.
The rest of the lines, usually defined by overwhelming mediocrity. Some have low-tier gems that may interest you, and they aren't necessarily "bad", but other lines are more deserving of your time, especially if you're stopping at tier 7.
British LTs: they aren't quite as bad as people say, but they're not great either. They're just "fine". Only starting at tier 7, this line is almost immediately disqualified, and in general it's the lowest priority LT line in the game, alongside the German LTs. Very low priority.
Chinese TDs: the definition of mediocrity. They're by no means bad, but the Russian TDs (particularly the SU-152 line) does everything better. Only grind if you have nothing else to grind.
Chinese MTs: just no. The tier 7 T-34-1 is a hidden gem, but tiers 8-10 are not worth the effort. If you really want the 121, then grind it via the light line and save yourself from a lot of suffering. There is exactly one niche use for this line: Object 279e missions, as the godawful T-34-2 is easy to ace as no one ever plays it. Avoid it.
French HTs (brawlers): the AMX M4 54 line is really only worth playing for the tier 9. The tier 8 AMX 65 t is extremely painful, and the tier 10 just feels mediocre. Not an awful line, but this should be of the lowest priority. Very low priority.
French TDs: the low tiers are all over the place, with some godawful tanks and some great ones. The tier 3 can be funny with its insanely small profile, and the tier 5 S35 CA (the "bathtub") is the best tier 5 TD in the game. However, tiers 4 and 6 suck, and the high tiers go a very unusual direction. Even among the most experienced, this line has few fans, but for the handful of us that understand how to play these, we adore it. As a new player, I recommend getting the tier 5 and stopping there indefinitely. Get the tier 5, but only push past it when you're ready.
Japanese MTs: the definition of mediocrity, with one exception: the tier 4 Ke-Ho LT is one of the best kept secrets in this game, and is a truly excellent tank. It's the only tier 4 non-scout LT that still feels very capable. The tier 7 is really odd, but as long as you can pen your opponents it can be fun to play. That said, there just aren't enough good tanks to recommend this line as a whole. The recently rebalanced tier 10 is what makes this line worth it, but you're a long ways away from that. Get the tier 4 LT, otherwise it's a very low priority.
Polish HTs: this line is actually pretty good, but only once you get past the tier 6. Even then, the tier 7 is not all that impressive. The top tiers are what make this line worth it, and in my opinion they are worth it, but as a new player I wouldn't worry about grinding for these at all. Wait until you're ready.
Which Path to Take?
When looking at the tech tree, you'll notice that many vehicles can be reached through multiple paths. Which is best? I'll go one-by-one, but I'm only covering the major branches as the low-tiers can get messy:
American HTs – T29 via MT or HT line: Shermans. If you choose the M6, then the T29's stock grind will be much less painful, but 14,000 XP is all you need to get the 90mm gun. As you're likely to already have the M4A1 Sherman, it makes more sense to research this via the Jumbo than to double back and suffer through the M3 Lee again just to take the T1 Heavy branch.
American MTs – T20 via M4A3E8 "Easy Eight" or M4A3E2 "Sherman Jumbo": Personal preference, but it depends on your plans for other lines. If you want to get the T29 and skip the T1 Heavy and M6, then the Sherman Jumbo is best. If you want to get the Jackson and skip the T40 and Wolverine, then go for the Easy Eight. If you have neither plan, then it comes down to which playstyle you like more. The Easy Eight is a more traditional medium, being a bit bigger and slower than usual in exchange for amazing gun depression and a solid gun mantlet. The Sherman Jumbo gets very thick hull armor, rivaling same-tier heavy tanks, and an incredibly tough turret option, but has HT-like mobility. Neither get amazing guns, and both are about equally capable for their tier.
American TDs – T28 via turreted or casemate line: Personal preference. It comes down to whether or not you plan to play the Jackson – if so, then the T25 AT (casemate line) makes more sense. If not, then the T28 Prot (turreted line) makes more sense – just keep in mind that when you get to the T28 Prot, you may find that you don't like it.
British TDs – AT 7 via HT or TD line: TD line, unless you are a dank memer and derive pleasure from playing one of the worst tanks tier-for-tier in the game, the Churchill GC.
British TDs – Challenger via MT or TD line: Personal preference. I go into detail in my section on the Challenger line (under "Best").
Chinese MTs – WZ-120 via LT or MT line: If you've finally decided that you want this line, then you must be at least a little masochistic. Temper your self-sadism and at least grind this through the LT line. The tier 7 MT may be good but the tier 8 MT will make you want to gouge your eyes out.
French HTs – ARL 44 via MT or HT line: Personal preference. I'd consider the BDR G1 B to be the better tier 5 tank, but after a few matches in the tier 4 B1 you might be willing to do anything to avoid playing it. The tioer 4 SARL 42 is thankfully a pleasant enough experience.
German MTs – Indien-Pz or Leopard PT A via LT or MT line: Personal preference. It really comes down to whether you do better in LTs or MTs. Personally, I give the edge to LTs, because this way you only have to grind one tier 8 to access both the Leopard PT A and the Ru 251. Sure, the high tier German LTs are not any good, but they'll be buffed someday… hopefully…
German TDs – Ferdinand via HT or TD line: For the love of god, pick the TD line. I don't care if you think you're saving time by playing the Tiger P, it won't matter when uninstall the game halfway through the grind in an attempt to save your sanity.
German TDs – Jagdtiger via Jagdpanther II or Ferdinand: Personal preference. It's widely agreed that the Jagdpanther II has more potential, but it's also harder to play, so less experienced players will likely prefer the Ferdinand.
Japanese MTs – Chi-Nu via LT or MT line: LT line, for the Ke-Ho. It really is a good tier 4 tank. That said, this is a low enough tier and an unimportant enough line that I can't say it matters very much.
Russian HTs – IS via HT or MT line: Personal preference. It really comes down to how much you hate the KV-85 – just remember that the KV-13 path will require substantially more XP.
Russian MTs – A-44 via HT or MT line: MT line (A-43), unless you're in the very rare situation where you enjoy the KV-85, haven't played the Russian MT line at all, and the only tier 10 Russian MT you want is the K-91.
Russian MTs – T-34 via T-80 or A-20: Personal preference. The A-20 line has more fun tanks but the T-80 line is also quite good.
Russian MTs – T-54 via LT or MT line: MT line. It's worth going back for the T-44 just to get the tier 9 Object 430 and tier 10 Object 430U.
One-Off and Skippable Vehicles
Finally, there are a couple of tanks that don't belong to a single branch, and other cases where you may have skipped a vehicle. Are they worth going back for? Again, this is worth going one-by-one, and forgive any repeats from other sections:
American – M4A3E2 or M4A3E8: You can't skip both tanks if you want the top-tier American MTs, but odds are you skipped both of them. If you skipped the E2 and enjoy tier 6, then it's worth going back for the Jumbo for its novelty. The E8 likely isn't exciting enough.
American – Jackson and T25 AT: Depending on how you went through the American TDs, you may have skipped both of these tanks. If you like tier 6, the Jackson is worth going back for, but I can't say the T25 AT is especially worthwhile.
British – Churchill GC: No, no, no, NO. Absolutely not. This tank belongs in a trash compactor. It truly is as bad as its reputation suggests, and should be avoided at all costs.
Chinese – T-34-1 and T-34-2: The first one, yes, the second one, hell no.
French – G1 R: An alternative path to the ARL 44. If you already got the ARL via the heavy line, there's no reason to go back to play any tank in the G1 R line, unless you really like low tiers.
German – VK 36.01 (H) and Tiger I: Yes, these are technically optional, because you can use the Panther to skip straight to the Tiger II. The tier 6 is nothing special, but the tier 7 is rather fun, and most players will want it in their garage just for the historical significance. You don't have to play these, but I think the tier 7 is worth not skipping.
German – Pz III/IV to VK 30.02 D: Another line that can be totally skipped, in this case by playing the German LTs instead. Concerns about the LT line aside, there are enough good tanks in this list to justify trying them out.
German – StuG III B: Actually, this one is worth it if you really like tier 4. It plays a lot like the Hetzer, losing half the frontal armor to be able to function like a regular TD.
German – Ferdinand: Not worth going back to play if you've already reached tier 9 via the Jagdpanther II.
Russian – T-50: A tier 5 light tank, which can be completely skipped in favor of the T-34. You should play the T-34 regardless, but this is a decent vehicle. If you skipped it, there's little reason to go back for it.
Russian – KV-13: A tier 7 MT that connects the IS line to the A-44 line. It's a pretty solid tank, but because it has to research laterally (that is, a tier 7 is researching other tier 7s), it adds a substantial amount of XP to a given grind. Few players will find themselves in a position where grinding this is convenient. Is it worth going back for? Not especially, unless you're fascinated with tier 7 mediums.
Russian – KV-2: Hell yes! You haven't played World of Tanks until you've played the KV-2. Don't worry about if research paths are redundant or irrelevant – the tank is fun enough to play for its own sake.