I think there are many parallels to Nazism and Stalinism. Both regimes had focus on a single supreme leader and despite Nazism being about having a "pure" Germany I think that it is ultimately to feed Hitler's growing hunger for power and so there it is the similarity to Stalinism which was largely focused on Stalin asserting dominance. Of course genocide is an atrocity that is for a much more in depth discussion but Stalin also went about killing many innocent people in the USSR, he targeted those who were intellectuals, those who were religious and those who opposed his rule. Even though Stalin did not conduct genocide, he's actions have caused the death of many who are innocent. Both men's ideologies were similar because they both allowed them to rise and gain power. To punish and get rid of those they did not like. Both of them also focused on propaganda to improve their public image and justify their terrible actions. So I don't think that one is worse than the other because, both of their ideals promoted the ideas of hatred and that in of itself qualifies as terrible. Arguing which one is worse is trying to justify that somehow the other ideology is in some ways justified than the other when in fact they were both carrying out similar actions to varying degrees.