Depends on what sort of a play style you're aiming for. Light tanks are good for scouting for spgs and medium tanks usually are the backbone of warfare.

I never tried russian tanks though but you should stick to medium tanks as you need a better turret to penetrate the heavy's armor

T-34 is not bad, can make money and is cheap to run. You'll get blown up by heavies in most games, and a nice arty shot will one-volley you. You also can't really hurt much except smalls and meds, and occasionally dent a low tier heavy in the back. Acceleration isn't that good too. But it's cheap

T-34-85 is the med tank sweet spot for making money. Still quite cheap to rep and arm, and can do some damage to most takes short of tier 9. Really good tank.

T-43 = barely break even -.-

somehow, my t-34 days were hell. imo it's kinda frustrating XD
anyway, i suggest you get the a-20, unless you got yourself a leo/other good lighty/pz3 as you'll more or less use em later on to support t-44. t-44 repairs is about 17k and with premium you barely break even... unless you had a good game