They both had incredibly evil consequences but there is one main reason why Naziism is more evil.
Naziism's sole purpose, was to exterminate the Jews. That was always Hitler's goal, and he admitted (To Islamic leaders) that the sole purpose of WWII was the extermination of Jews.
Communism's sole purpose wasn't the extermination of a people. But, yes, in order to accomplish its evil and twisted goals, millions of freedom loving people had to be slaughtered.