Hitler was a National Socialist, Stalin was a Communist, both espoused their form of Socialism. they had no problem committing mass-murder, Stalin far outnumbered Hitler with regards to victims killed. Hitler was a selective murderer, his killings were mainly based on race, Stalin however was non-selective, he would kill for various reasons,  showing no prejudice. Both were disgusting tyrants, hopefully consigned to the dustbin of history.

One can dress it up under whatever name one wants but to my mind Stalinist Communism and Hitler's National Socialism were similar sides of the same totalitarianist coin. However a key difference was that, while both regimes strenuously promoted a cult of personality of the supreme leader, Stalinism fundamentally had an ideology that existed independently of Stalin himself, while Nazi ideals were almost by definition whatever Hitler said they were, whether that was in 'Mein Kampf' or subsequently by simple decree. Furthermore the Nazi policy of Lebensraum was fundamentally about subjugating/removing 'lesser peoples' to allow 'Die Deutsche Volk' to be able to fulfill their supposed manifest destiny ... while Stalinist expansion was ostensibly about freeing all workers in all countries, equally, from the international 'Shackles of Imperialism'. Nevertheless in practice both ideologies generally resulted in a similar armed invasion of neighbouring sovereign states and the forced subjugation of their peoples ... to be followed by the systematic elimination of those that would not conform.

In theory the Communist ideology may have stood supreme, but in reality Stalin had full control. Hitler however, although he was the final arbiter, was very sensitive to German public opinion, an example of this, was the decision to officially end the the Euthanasia programme, started in 1939, terminated in 1941.

Numbers.


Stalin could afford to lose 30 million. Hitler couldn't. Hitler cocked up by slaughtering people who may well have fought for him (in Ukraine for example).