I definitely put all three in the same category. Stalin was probably less bad than Hitler (he killed more people than Hitler did historically, but imagine the body count if Hitler had won); but it's not easy to choose among totalitarian regimes -- or aspiring totalitarian regimes, in ISIS' case.
>>clock_+(OP)
>he killed more people than Hitler did historically
Only when counting famines and a civil war type situation among his casualties. He killed much less than Hitler otherwise (which would still be a lot).