@ Loftus99 I know this is a rather old statement, but misinformation in your post still really needs correcting. It was in WW I that the Tsar sent the Russia troops, weaponless and foodless into the front, not the communist regime.
I'd have to go with Stalin, while both he and Hitler had some very solid policies during there times in terms of reforming the state of their countries, Hitler was not only more unstable, as well as a Facist. I'd rather live under Communism then Facism. Good policies included the Nazi Youth groups, Five year plans, improving education systems in both countries and massive scientific advancements. The real issue with Stalin's Russia in my mind that they were involved in a war communist economies don't really have room for unnecessary drains on resources that need to be used to keep everyone fed and in good shape.
To those of you quoting, the Ukraine Famine, and the Holocaust as reasons for these two being evil, I wonder if you've ever looked much into the history of India under Britain, with the East India Company? The Spanish in South and Latin america? Any of the European powers in Africa? There were tons of atrocities happening during that era does it make any of them less vile? Of course not, however that was the reality of the time and it can hardly be judged by todays morals which are radically different.
As for the Great Purge, and the Night of Long Knives both of these events are a tragedy that you see repeated in regimes where a single leader holds power to this day, it bred of paranoia and a desire to stay where they are. In that regard it seems most dictators are the same.