I'm surprised there can even be a question whether Stalin was worse. If you die as a Muslim, insha'Allah you've won, you go to jannah which is the success.
If you get put in a communist re-education camp and they brainwash you into becoming an atheist, that is way scarier than just getting killed. I think death is a mosquito bite compared to getting brainwashed into becoming an atheist.
I don't hate Hitler the way I hate Stalin. Read about the history of what happened to Muslims in the Soviet Union.
And let us not hold this materialistic unreligious view that dying is the worst possible thing. When I think about Stalin's war on Islam- I feel bad for the Muslims who were killed, sure. But that's not what angers me the most. What angers me even more is the effect that continues to this day of how Soviet Muslims were mass-brainwashed into becoming largely irreligious. Many Central Asian countries to this day are irreligious because they basically had their iman stamped out of them.
I remember I had a Central Asian co-worker. It was Ramadan and he openly wasn't fasting. He didn't care, he had no shame. This yes I believe is a direct result of Communism in his country.
In my view, Islam is more important than the life itself. If someone gives up his own life to defend Islam- hero. If someone gives up Islam in the interest of dunya- I think he is scum.
I cannot think of much more evil than mass brainwashing Muslim populations to give up their religion. Stalin undeniably waged war against Islam. I don't know of Hitler going to war to wipe out Islam.
The history of Muslims under Soviet Communism is fascinating and I recommend this book to everyone
Many great Muslim scholars came from Central Asia. Thinking about what was done honestly makes me angry.
edit: btw Amazon has used copies that are way cheaper than the $100 copies