The USSR was terrible. Remarkably, the Nazis still managed to be substantially worse.
As one example there's the Hunger Plan. Hitler's defeat stopped him from executing it, though they had started. He planned to kill 35-41 million people in eastern europe via starvation and take the land for Germany.
The USSR equivalent, Holomodor, killed 3-5 million, and was fully executed. Horrendous. Not as bad as the hunger plan.
And that was not the only Nazi mass death plan....