It got to the point a long time ago I started being amused about people claiming, "The Holocaust of my people was worse than the Holocaust of your people!"
Jews tried to claim six million of them were killed during World War I (no, not just World War II, but also World War I). Yet some of the worst mass murderers of the 20th Century were Jewish - look up Genrikh Yagoda. And Communism was originally called "Jewish Bolshevism."
And take a look at the Holodomor.
The worst, per capita, was Cambodia. The worst, in terms of numbers, was what Mao Tse Tung did to China - on top of what the Japanese did.
By the way, I've had people tell me there were 20,000,000 Indians in north America. Really? Hunter-gatherers who sometimes grew corn? There were about a million, and most of them died from European diseases to which they had no natural immunity (the story about Indians being given smallpox infected blankets is pure fantasy). In combat about 2000 Europeans died and about 2000 Indians.
Chinese Holocaust = 60,000,000
Russian Holocaust = 30,000,000
Congo Holocaust = 10,000,000
Ukrainian Holocaust = 8,000,000
Jewish Holocaust = 6,000,000 (Disputed)
Cambodian Holocaust = 4,000,000
Armenian Holocaust = 2,000,000