Communism has killed far more people than Nazism. If you go by the number of deaths, communism is much worse. Stalin, Zedong, Tito, Pot, Sung, etc... were all monsters. Of course the difference is that Nazism as an ideology has been outlawed whereas communism, despite the fact that it has been attacked by the West and fervently opposed by many, continues to be a practicable and accepted ideology in some countries.