I honestly have no idea why people prefer the IS-2 over the tiger.
Except for the IS-2s higher armor, the tiger is pretty much better in every way.
IS-2 has slightly higher pen while the tiger has a higher rate of fire thus making it better againts tanks ( or at least all allied tanks except IS-2) , tiger also faces significatly weaker AT than the IS-2 and tiger is also significantly better againts infantry.
IS-2 is more durable, but that's about it...
