I'll do tier 5 onwards since I don't play lower tiers. Not counting premiums. Just my opinion.
Tier 5:
Medium:
t-34: Soviet medium tank with a very fast firing gun, good gun handling, and decent mobility. Also leads to some of the best medium tank lines in the game (OBJ 430U and OBJ 140)
m4a1 Sherman: a fun derp tank that can one shot most equal and lower tier tanks. Decent mobility and excellent gun depression. Also leads to one of the best medium lines.
panzer IV: similar to the M4. The derp on this tank fires faster but does less damage, which can be good for permanently tracking enemy tanks in comparison to the M4. Leads to two lines, E-50m and Leo, which are both good in different ways.
Heavies:
KV-1: a slow and excellently armoured tank with 3 gun choices. The 85mm gun has good alpha damage and decent damage per minute. The 57mm has bad alpha damage but excellent damage per minute. There's also a derp that isn't too great but it's an option. Leads to the most beginner friendly line in the game, the IS-7 line.
KV-1s: similar to the KV-1 but has worse armour and better mobility. Also, I think it doesn't get the 57mm gun. Also leads to the IS-7 line. Will be moved to tier 6 in the future, but not sure how it will play then.
Tank destroyers:
T67: Really hard to play for beginners, but ridiculously overpowered if you understand the game mechanics of view range and camouflage very well. Very fast tank with great concealment and a fast firing gun. Also has a turret, which is always an advantage.
Wolverine: slower than the T67, but has better gun handling. Also has the option of a derp gun which can be really fun. Better for new players.
Light:
T-50: A very fast, nimble, stealthy tank that can scout quite well. Only downside is that you have pathetic alpha damage. You need to penetrate 30 shots to kill a Tiger. Leads to one of the best light tank lines in the game too.
Chaffee: The best scout at tier 5 and great for learning how to scout. Good view range with binos (or with optics if you have a great crew), very stealthy, quite nimble. Great gun handling as well. The line it leads to is pretty underwhelming except for the T49, however.
SPG:
M41: none of the tier 5 artillery are good except for the premium french artillery. However, this leads to the best artillery line in the game overall, so I recommend it.
Tier 6:
Medium:
T-34-85: best all around medium at tier 6. Good alpha, decent DPM, good gun handling, and enough turret armour to bounce low penetration guns while being quite nimble.
Cromwell: a very popular but also very overrated tank. Amazing mobility and DPM, but the gun handling is abysmal. You cannot snipe or fire on the move. Overall a solid tank still.
VK 3001p (though it will be designated a heavy tank soon): Amazing alpha damage of 220, decent DPM, decent armour, and decent mobility. Overall a great brawling medium tank. Leads to the German heavy Maus line.
strv74: no armour, meh mobility. However, you have 15 degrees of gun depression and godlike gun handling, seriously some of the best at the tier. Great tank for sniping and for abusing ridgelines. The line it leads to is pretty solid but hard to play.
Skoda t25: a very fast tank with a nice 3 shot autoloader. Doesn't turn well and has no armour, but the burst damage and decent DPM makes up for it. The line itself has great tier 9 and 10 tanks, but the grind to get to them can be painful for some.
Heavies:
KV-2: the king of derp. A very fun tank with a devastating deep gun that some tier 8s fear. Great fun and everyone should have one.
T-150: a very heavily armoured tank with a fairly hard hitting gun. Great for learning how to sidescrape and angle. Leads to the IS-4 line, which is awful and should be avoided, and the double barrel heavies, which are good at tier 8 and 9.
OI: a slower, more heavily armoured KV-2 with a shittier gun. Can be quite overpowered when top tier, but it's not as good as the KV-2. The line it leads to is also garbage.
Tank destroyers:
Hellcat: very fast in a straight line, stealthy, and has a hard hitting gun and a turret. Great combination. However, its reverse speed sucks, which means you can't back off from danger easily, and it has no armour. It also cannot fire on the move due to poor gun handling.
Jackson: I prefer this to the hellcat. It's much slower, but not awfully slow, and has a better version of the same gun, with much better gun handling and better DPM.
su-100: a very stealthy TD with an extremely hard hitting gun for the tier. No turret, sadly. Leads to one of the best tank destroyer lines too, the OBJ 268 V4.
Jagdpanzer IV: a stealthy TD with decent mobility. The gun is amazing, with decent alpha of 220 but amazing DPM. The JPE100 line is not competitive but can be fun.
Lights:
T37: decent viewrange, decent gun, and alright camo. Great for learning how to scout.
AMX 12t: Really hard for beginners. The first true autoloading light tank, it has an alright clip size but a long reload that can be hard to manage. Also has amazing concealment, so it can be an effective scout. Mobility isn't greay compared to other lights of the tier. Leads to two of the best light tank lines in the game, the AMX 13 105 line and the EBR 105.
SPG:
M44: Ridiculously broken. Very mobile, great gun arc, very fast firing. Even tier 8s loathe playing against these. Also a great credit maker as it literally does not get gold/premium rounds.
Tier 7
Mediums:
T20: Pretty good alpha of 240, amazing gun handling, excellent penetration, great mobility, and great camo. An excellent tank and my favourite tier 7 medium. However, its DPM is quite poor and it has no armour.
Leo: A very underrated tank. It has the option of two guns, a fast firing gun with great gun handling and DPM but low alpha, or a big alpha gun with band gun handling and DPM. Pretty good mobility, good gun depression, and decent camo. No armour.
Heavies:
T29: The best tank in the American heavy tank line. Amazing turret armour plus a hard hitting gun. A hull down monster at tier 7. The rest of the line is pretty bad, however.
Tiger 1: A noob trap. In the game, the Tiger has absolutely no armour, but it has an incredible gun with amazing DPM. Played more as a support and sniper tank.
IS: Very fast and mobile heavy with a very hard hitting gun. No armour, however. Great for peaking, taking a shot, then retreating back into cover.
Tank destroyers:
Challenger: Another underrated tank. A pretty stealthy, decently mobile TD with a turret and a fast firing gun with great DPM. The rest of the line is also fun, ending with the shitbarn, which can one shot most tanks.
SU100M1: decent armour, decent mobility, and decent gun. Can brawl when top tier and support when bottom tier.
Lights:
T71 DA: Very nice autoloader with good clip potential and decent DPM. Very nice view range. Not a great scout, however, with poor camo rating.
AMX 13 75: Also an autoloader, but has a smaller clip with a shorter reload. Easier to manage but less burst overall. An excellent scout with great camo rating and decent viewrange.
T71 CMCD: Single firing version of the T71. Excellent gun handling and DPM. It's as effective a scout as the DA.
WZ-131: Has quite a hard hitting gun for the tier with 200 alpha damage,but has poor DPM. Excellent scout with incredible camo and decent viewrange. Also, like most Chinese tanks, it has poor gun depression.
SPG:
GW panther: Great gun arc, great mobility, decent alpha damage and a good reload time. The only good tier 7 SPG.
Tier 8
In this tier, the premiums are much better than the standard tanks. But I'll stick to non premium tanks.
Mediums:
P44 Pantera: A very fast tank with a very nice auto-reloader. Extremely flexible tank but quite hard to play.
T-44: The best all rounder. Decent gun, decent mobility, decent armour. This tank does nothing poorly.
Heavies:
IS-3: Quite mobile with an incredible gun. The armour works when top tier but it's quite poor when not top tier.
IS-2-II: Decent mobility, quite poor armour, but an incredible gun. It is a double barrel tank, so it can fire both at once. Even in single fire mode, it has excellent gun handling and good DPM. Nice gun depression too. A very solid tank but a bit harder to play.
VK1001p: A very, very well armoured superheavy tank with two gun options. One is a faster firing gun with low alpha but great DPM, and the other is a very high alpha gun with poor DPM. Very slow but undoubtedly the best armoured tank at tier 8 (if you don't count premiums, in which case, it's the Defender).
Caernarvon: A hulldown tank with very poor hull armour but a solid turret. The gun is incredible, however, and bordering on OP. It has low alpha but has DPM that rivals tier 10s.
Tank destroyers:
Charioteer: Decent mobility and a turret, which automatically makes it a great TD. It also has solid camo rating. The gun is decent alpha with excellent penetration and high penetration HE rounds for softer targets. Gun handling sucks, so you can't fire on the move.
UDES 03: Amazing speed forwards and backwards, 70 and 50, and incredible camo rating. In fact, the best at tier 8. The gun is decently has firing with decent alpha, but its strengths are in having the best penetration at tier 8 (288) and literally the best accuracy in the game (0.25). However, this tank is pretty inflexible due to its siege mode mechanic and is relegated to just sniping.
RHM borsig waffentrager: a slow turreted TD with amazing camo and a choice of two great guns. One is a 128mm gun, which hits hard (490 alpha) and has amazing DPM and good accuracy. The other is a 150mm gun that hits REALLY hard (750 alpha) but has poor penetration and accuracy.
Lights:
BC12t: Another autoloading light with great gun handling, decent clip size, but rather poor DPM. Great at assassinating low health targets. Excellent scout with amazing camo rating and decent view range.
WZ-132: A very nimble and very stealthy tank with a pretty hard hitting gun for a light tank (250 alpha). An excellent scout with great camo and decent view range. And again, since it's Chinese, it has poor gun depression.
SPG:
M40/43 or whatever the American one is called: Pretty good mobility, great gun arc, and very hard hitting.
Tier 9
Mediums: lots of competition, really depends on your playstyle.
Skoda t-50: My favourite tier 9 tank. Decent mobility. The gun is an excellent autoloader that unloads very quickly and reload very quickly. No armour, however.
M46 Patton: hull down medium with excellent DPM and gun handling
Leo PTA: Amazing sniper with no armour. Has really nice alpha damage of 420 and high penetration HE rounds as well.
standard B: A very flexible auto-reloader. Good mobility, good gun depression, good gun handling. Just an amazing tank but also quite hard to play well.
E-50: also a sniper medium with great DPM. Against tier 8s, it can play as a heavy tank.
AMX 30: Decent gun depression, excellent speed, excellent DPM. A decent turret too, but you can't rely on it. A very solid all rounder, but I don't think it's as good as the Patton.
T-54: Great all rounder with fairly good armour, fairly good mobility, and a great gun with excellent DPM.
OBJ 430: Plays like a heavy tank. Amazing armour with a hard hitting gun. Gun handling is pretty bad though and catches on fire a lot.
Heavies:
WZ 111 14: Decent armour with excellent mobility and a very hard hitting gun. Can play almost as a medium tank.
T-10: Similar to the WZ, but has less alpha but better DPM and gun handling. Kinda hard to play but an excellent heavy/medium hybrid.
Conqueror: A very slow hulldown heavy tank. The hull armour is trash, but the turret is amazing. The gun is incredible too with excellent DPM and gun handling and also high penetration HE rounds.
AMX M4 51: Very well armoured, decently mobile, and has two gun options. One is a faster firing gun with decent DPM and better penetration. The other is a very hard hitting gun with lower DPM and quite poor penetration.
IS-3-II: Another double barreled tank. Decent mobility and nice gun depression, alright turret armour but quite a poor hull. Where this tank shines is the gun; it has quite good gun handling, and when fired together, it has the highest alpha at tier 9 (780). Quite difficult to play, however.
Lights:
AMX 13 90: Very stealthy tank with a nice clip. Can scout really well with good camo and good viewrange. Can assassinate low health targets very well.
The rest of the tier 9 lights suck.
Tank destroyers:
tortoise: very slow but also very well armoured. The gun is very fast firing with the second best DPM in the game.
waffentrager pz IV: plays pretty much indentically to the borsig. A stealthy turreted TD with no armour. The gun has quite good alpha and DPM. The best sniper at tier 9.
t95: Very slow, EXTREMELY well armoured. The gun is also very hard hitting with 750 alpha and excellent penetration. A very fun tank.
t30: Can play like a hulldown heavy tank. The turret is fairly well armoured but the hull is trash. The gun is a shittier version of the t95's gun. It's not a very mobile tank, but it's much more mobile than the T95 and much more flexible due to its turret.
SPG:
M53/55: Good mobility, great gun arc, and quite hard hitting. Considered by many to be the best artillery in the game despite it not being tier X.
Tier 10
Mediums: again, a lot of variety.
Progetto 65: A very flexible medium tank with its auto-reloader. Good mobility, good gun depression, good gun handling. Just an amazing tank but also quite hard to play well.
TVP: Has a fairly small clip but unloads it very quickly and reloads very quickly too. Much better mobility than the tier 9 as well. Quite a flexible autoloader but not as much as the progetto.
obj 140: great all rounder. Pretty decent armour and mobility, excellent gun with great DPM and gun handling.
obj 430u: Overpowered heavy tank. Incredible armour with a hard hitting gun, but it has quite poor gun handling. Another thing is that it has one of the best camo ratings of any mediums as well, so it's an OP heavy that's also very stealthy.
leopard 1: Amazing sniper with no armour but incredible mobility (it's the fastest medium tank in the game!). Has really nice alpha damage of 420 and high penetration HE rounds as well. Also quite hard to play.
M48 Patton: hull down medium with excellent DPM and gun handling. Unlike the tier 9, this one actually has quite good armour as well and also the best view range in the game (420).
STB-1: amazing hull down tank with 14 degrees of gun depression in its siege mode (hydropneumatic suspension activated when it'a going slowly) and 8 otherwise. Godlike DPM and quite a nice turret as well.
Heavies:
OBJ 277: Extremely mobile heavy with a very hard hitting gun with incredible gun handling. Hull armour is kinda poor but turret is excellent.
WZ 111 5a: similar to the 277. Has a weaker turret but has better DPM and gun depression.
Super Conqueror: A very slow hulldown heavy. The hull armour is trash, but the turret is amazing. The gun is incredible too with excellent DPM and gun handling and also high penetration HE rounds.
Tank destroyers:
Strv 103b: A pure sniper tank that also utilizes a hydropneumatic suspension (siege mode). Really fast backwards and forwards and has incredible camo rating. Its gun has some of the best DPM (albeit poor alpha damage) and the tied best accuracy in the game. Undoubtedly the best sniper in the game. Pretty inflexible however, relegated to just sniping.
OBJ 268 v4: A mobile, very heavily armoured assault TD. Very easy to play and plays like a heavy rather than a traditional TD. Its gun is quite poor compared to other tier X TDs but it's still a great gun.
Lights:
EBR 105: The best light tank in the game. It's the fastest tank, 95 kph forwards and 70 backwards, has the best camo of any tier 10 light tank, and if you push it to its maximum, can have 470 viewrange*. The gun has godlike gun handling and high penetration HE rounds, but it has quite poor DPM and abysmal penetration. Though it is the best light, it's actually extremely difficult to play really well.
*That's with improved vents, improved optics, BIA, situational awareness, recon, and the directive that improves your optics, and strong coffee of course. 470 is the absolute max even theoretically possible.
AMX 13 105: Has the most dangerous gun of any tier 10 light tank, having a 3 round autoloader with nice burst and a short reload. The damage potential is amazing and it's a great assassin. A pretty good scout as well with good viewrange and camo.
T-100 LT: The best passive scout in the game, with third best camo of any tier 10 light but poor viewrange, but that can be boosted a lot with crew skills and equipment. The gun also has godlike gun handling and it's just good at harassing enemy tanks for small damage. The armour is quite troll as well, always getting random bounces.
SPG:
conqueror GC: Incredible alpha damage and gun arc but what makes it really great is the shell trajectory; the shells loop over and hit the top of enemy tanks, dealing more damage as roof and engine deck armour is quite poor. It's quite big and slow though.
