Mao was 50,000,000 conservatively. Nobody really knows, I suppose.
If you look at direct casualties in all wars, Communism killed more people.
If you look at direct and collateral casualties in all wars, war is slightly ahead of communism in killing people.
That’s saying something, since Communism did all that in under 100 years.
In either case, he makes Adolph Hitler look like an underachiever. Compress it into the century or so that Communism has been around and tyrants like Genghis Khan and Tamerlane look even more like pikers by comparison.