Got the IS-2, T-34-1 and the premium T-34-3.
Never played the russian IS, but they don't seem to differ that much from each other.
T-34-1 is imo one of the best Tier 7 Mediums, as long as you don't show its hull, since its really weak.
T-34-3 on the other hand is pretty difficult to play, but as soon as you know how, itÄs also nice.
One big advantage of the chinese IS-2, or specifially the 122mm gun, which you can also use on the T-34-2 or is used on the T-34-3, is the fact that it does 250mm of Penetration with premium ammo, unlike the russian with its 217 or something.