I'm going out on a limb and say Hitler's more interesting than your example, Stalin, for a couple of reasons. This will probably contain some factual errors since it's mostly based on truthiness on my side:
Hitler was elected, Stalin grabbed power.
Hitler had (at least in the beginning) people who loyally stood by his cause. Stalin had people doing his bidding because they were afraid. In other words, Hitler had charisma (terrible word to use about such an awful man) and knew how to bind people to him personally.
Stalin joined the fight against Hitler (after Germany violated the non-aggression pact). Allies needed him to win the war. The enemy of my enemy is my friend and such. Even though he did many terrible things, 'at least he helped us out in our time of need' - forgetting that was out of self-interest too.
Stalin's victims were mostly among his own people. Things that happen close to home have a much bigger impact on how we feel. If we go by the numbers, we'd say Stalin was responsible for about 15 million deaths (or up to 60 million according to other sources in Sovjet Russia.
Scientists are predicting the future will be much more futuristic than originally predicted