Reasons for differences i would say comes down to a key point: Ideology and the nature of the men as Ideologues
Stalin was ruled less so by ideology than Hitler but still enforced policy of agrarian collectivisation and advocated for the destruction of capitalism within Russia. He was more of a pragmatist. With the opportunistic forethought of Stalin and his ability to step aside from communist tendencies to focus on the political moves best for Russian growth, Russia rearmed for war in just over 2 years compared to Germany's 5 or so (I think) - note, this was even through the Great Purge of the Russian military, where Stalin removed 90% of his high ranking military officers - Thus, I believe his terror was more confronting, as he was not tied to any certain ideology but rather to his own intuition and beliefs for a stronger Russia, even if this was at the expense of the population and short term strength. The public show trials, hangings, persecution and complete indoctrination of the people was not fully experienced in the Third Reich.
But:Hitler had a terror of his own, though i believe this was more neurotic: I think it is fair to say that in Russia, they trusted and loved Stalin but I just feel that in Germany it was truly genuine. The people voted him in (despite backroom deals) and the majority of policies he outlined for Germany were executed - although there was some terror was on the home front: take the Gestapo, labour camps, widespread propaganda, they were all terror tactics to enforce conformity and gain support for the Nazi's. But because of Hitler's ascension to power and the way in which the terror was not focussed upon the people but the enemies of Germany, the terror was different.
the people were unaware of the Terror inflicted upon the Jews: but I don't need to explain how bad it was. 6 million deaths is enough to show the extent of the violence - but again it comes down to ideology and Hitler's guiding beliefs of social darwinism and lebensraum in the east. To him, gaining territory was a goal established from party infancy and was a fixated plan - if the Jews needed to be killed and if terror needed to be used, it was an easy decision.
sorry, I went on a mad tangent and it probably doesn't make 100% sense - what do you guys think?
This is a difficult question. In general, Hitler and Stalin resorted to similar tactics for their goals (starvation, rape, execution, imprisonment, etc). Both used literature and propaganda as tools. Statistically- Stalin has ALOT more blood on his hand than Hitler (imo)- even if Hitler's philosophy is perceived as more barbaric and offensive. Stalin strikes me as adaptable, revolutionary and forward-thinking, whereas Hitler is impulsive, emotional and inspired by romantized notions of historical events (The Roman Empire). So, I suppose the question you want to ask in your homework or research is this:
How did Hitler and Stalin exploit opportunities that were given to them?
Simply put, Stalin had more opportunities than Hitler to inflict terror and violence. Not only was he in power longer (and could amass more followers, produce excessive propaganda, fulfill plans of elimiting enemies) but he encouraged Kim Il-Sung to invade South Korea, (which resulted in China deciding who would win). Stalin's reign of terror should not be limited to the USSR, but also parts of Europe and Asia- politicans and people in power listened to Stalin. Hitler? Not so much. Hitler found allies in Japan, Italy, Hungary, etc- but all were challenged and defeated- giving huge blows to not just the Third Reich, but the ideology behind Nazism and Fascism.
My point is that Stalin was given more time to be an awful human being than Hitler. With Stalin- I feel he left a stronger mark and haunted Eastern/Central Europe and Asia in ways that many historians do not discuss. Hell- as long as people are unwilling to discuss Stalin's reign of terror, the more I am convinced that its not over.
Sorry for my convulted thoughts, hope this was sort of understandable.