Hitler was mass-murderer crazy -- that is, he would go into a place and spray everyone there with bullets.
Stalin was serial-killer crazy -- that is, very secretive and furtive.
Hitler never had the atomic bomb, so we don't know definitely if he would've used it. But I believe he would have.
Stalin did have the atomic bomb, but he never used it -- and neither did any of the other men who followed him as rulers of the Soviet Union.
So you could say one thing about that. The communists were tyrannical bastards -- but SANE tyrannical bastards.