Some examples of the WW2 soviet tank lineup:
KV-1: early war heavy tank, slow, had the disappointing gun of the T34/76, but very well armored.

KV-2: KV-1 hull with a 152mm cannon, well armored, good firepower, but the short barrel of the cannon may cause diffculties in the long range firepower, also a big butt target.

KV-85: KV-1 fitted with the T34/85s cannon, well armored, has good low range firepower

IS-1: a new, heavily armored hull fitted with the 85mm gun. Only was in production for two months.

IS-2 (1943): IS-1 upgraded, had 120mm of sloped frontal armor and a 122mm monster cannon. A big, slow beast, but only carries 28 rounds and takes almost a minute to reload... so if you miss, you might be in trouble.
IS-2 (1944): redesigned, even more effective frontal armor

SU-85: the "jagd-T34", fast and acceptable firepower, the same 45mm armor as the T34's hull but a bit less sloped. Would make a good non-perked tank destroyer.

SU-100: SU-85 with a 100mm monster cannon, what had more AP ability than the IS-2's 122mm one...

Edited to make Mainer happy

I give a +1 to any of those
