I'm gonna pull the obvious Communism has killed more than Nazism.
Done.
I'm gonna pull the obvious communism is not a political ideology that believes in killing innocent people and that Nazism is.
Standing for Nazism makes you a fascist who believes that a large number of people do not have the right to live a free and decent life (at the very least). Standing for communism makes you someone who believes that all people should be equal at the base level.
You can be a communist and a pacifist, you couldn't be a Nazi and a pacifist.
Furtheremore there has never, and never will be, a true communist regime in any country anywhere in the world. Sadly communism doesn't actually work in practice.
Also I think you'll find that democracy has killed more people than either communism or nazism.