I will generally avoid US vehicles myself, but I need the Russian mediums, because German and American alternatives are of no contest. Hell when meeting a T-54, an IS4 is no contest.
While Russian heavies are good brawlers, they just don't have that awesome firepower of American heavies. Besides IS3 is crap, it's a weak link between IS and IS4 which are both excellent. Also KV and KV3 are so slow, that it really is a pain to grind them.
However my biggest dilemma is this: Russian or German TD? Russian TD can one shot things easily with their insane guns if the hit something, while German TD will need more shots as not all of them might penetrate, but they can easily hit a viewport of a tank that stands behind a window on the other side of the map.
Even worse, American TD will be announced and nobody has any clue how good or bad they are.