By the way, for me this is like moving a pawn in the opening gambit. Go ahead, answer.
So I'm wondering. Who gets to decide who "wins"? Is it when one side concedes defeat? You know that ain't gonna happen. Is it when "disinterested 3rd parties" decide who wins? There ain't any here. Is it when the other side mentions Nazis? In that case I think you lost with your opening statement that 20th Century atheists killed 180 million people. (I assume you're including the Nazis in order to come up with the extra 80 million over & above the Communists' 100 million.)
The Nazis were certainly atheists also. But you forget one of the most murderous atheists around by just concentrating on Communists and Nazis. You forget Africa. Remember Idi Amin? Some 4-5 million in a pretty small country. Remember Rwanda a few years back - 2-3 million. The present war in the Congo has killed a few million by itself. Then there is also Somalia with deliberate starvation, there is Nigeria, there is Ghana, and numerous other places in Africa where wholesale murder has been the order of the day since it gained its independence from the 'evil Europeans'.