What med line should i go? HELP

Hello,i'm a player that came back to WoT after a LONG break. I've been playing mostly on heavy tanks and maybe sometimes tank destroyers,but i want something new.
I think that grinding some mediums would be interesting! I know that everyone say that Russians are the best but is it true?
Also i didn't really got to the higher tiers, like 6 or 7 are my max for now :/, so please don't complain about like tier 10 becouse i won't really need that knowledge for now.
I like having some armor and good gun that can really hurt
But i learn of course!
I thought about it and i saw Americans really cool,fast and just fine and easy to play.
I should also say that i have 1.500 battles but i wasn't playing for like 2 years or so.
So treat me like a pretty new player.

Thanks for all advices, and sorry for all mistakes!
English isn't my first language(+ writing this on mobile), but i really needed help so cheers! 🙂