This question is often being asked in a more common form: what is worse - Nazism or Communism? But the reply seems to be simple, maybe too simple. The most consequent and uncompromising Marxists-Leninists-Stalinists, well-known to the world as Red Khmer, succeeded to almost exterminate the total number of town dwellers in their own country Cambodia within a few years only. Not a single Nazist would ever have thought or dreamt of something like that.
The question of comparing Hitler's and Stalin's regimes is not that easy to clarify, although at first sight a comparative "moderateness" of the Nazists becomes evident.
In Hitler's Germany nothing at all happened that was similar to the Great Terror - the Nazists only killed and sent to the camps real antagonists, and as soon as the interrogators of the Gestapo had convinced themselves that the charges brought against the accused were unfounded, they immediately discontinued the tortures and set him free. Exceptions, such as the Dimitrov action, only prove the rule. In Germany they did not make any attempts to enslave and oppress farmers.
But Hitler was merely the "executor" of this world war, while the true organizer was in the Kremlin. Already long ago historians furnished reliable proof of the fact that Germany was not at all prepared to go to war. From the very beginning the German strategists, and presumably the Nazi leaders, as well, had realized how fatal the war would turn out for Germany.
From the very first day of war on two fronts (in fact, they were a lot more) the theorists of war were aware of the fact that Germany was condemned to meet with a devastating defeat. Well, then, when they panicked, the Nazist provoked and started the genocide, which was totally lacking in rational foundation and yet did not delay the collapse for a single moment.
Strictly speaking, the "race theory" did not serve the Nazis as "guidelines to act", but purely and simply as a ritual, propagandistic cloak. It is characteristic that the inter-German Slaves - Sorb Serbians (in German Sorbs or Wends) - were not exposed to any oppressions under the Nazi regime, until the spring of 1945. It even seems that the Nazi leaders themselves did not take the "race theory" for serious. And not all of them were so uneducated not to know that gipsies, who were sentenced together with Jews, were real Aryans and besides the only ones in Europe!
On closer inspection of the Hitler system details emerge which give food for thought.
Comparing the Nazi camps with the Soviet ones we notice a striking analogy of the detention camps to those earlier Soviet camps that were yet called CONCENTRATION CAMPS: Kem'per Point, SLON (Solovetsk Special Purpose Camps) ... The organization following the example of the army, with unprecedented drill, (literal) slavish obedience, discipline, the awareness of completely useless work, such as carrying stones to and fro...
In the 1940s; however, the Nazi labour camps started becoming more like the Stalinist ITLs (reform labour camps). And this is what happened to the Soviet kolkhoz farms during Hitler's occupation: in the Pskow and Novgorod regions, in Belorussia, they were allowed to liquidate them, for they could not take anything with them anyway, and on the Ukrainian black earth - for no reason at all. Therefore the occupying powers, indeed, removed one "contingent" after the other. But the tendency is obvious. Apparently, they considered the procedure of cleaning out the kolkhoz farmers as being much easier, compared to the free Volhynian peasants.
We get the impression that the Nazi regime developed into one and the same direction as did the Soviet, with a difference of time. And that is quite natural considering its "youth". For in the USSR, in the 1920s, there were no lumbering camps, no kolkhoz farms, and there still ruled the freedom of trade! The Nazi regime, in general, is rather similar to the NEP (= New Economic Policy). But it simply did not succeed in developing according to its interior logic and in becoming mature. Fortunately, history did not give this process of development more time. But, unfortunately, in this case only.
This probably explains the historical immaturity, the non-completion of the seemingly "moderate" Hitlerism, compared to Stalinism. And we tend to simply reply to the question of "What is worse - Stalin or Hitler": both are worse.