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.