To those saying the German TD's are well represented, this is patently untrue. The 3 TD's we have only came into service in mid-late 1944, and represent roughly 1/30th of the German armored forces for the entire duration of the war.
The StuG series, on the other hand, represents about 2/7'ths of German armored forces (much more, if you don't count Panzer II's, and Pz 35/38(t)'s, and early/prototype variants of the Panzer III and IV, closer to 1/2, actually).
The SU-100, on the other hand, represents only around 1.5% of Soviet armored forces for the entire duration of the war, and only saw service from 1944 onward.
Basically, you are advocating an inferior Jagdpanther with a red star on it. Virtually useless for special events (given it has less than a year for which we could use it, and GV's are almost never used in special events), and beaten out by the Jagdpanther at the only thing it would be really good at.
The SU-76 would be most representative, overall, though the SU-85 would still be better as well.
As to the IS-2, it would blow as an anti-tank vehicle. 20 seconds to reload, just a poor ballistic coefficient, standard 2.5x optics, and awful armor penetration for how big of a shell you're throwing. That being said, you could kill the town in about 10 shots.