Look at what Hitler did, and I don't mean the Holocaust. This one man brought his whole country out of debt, he united them under one banner, he created the jet engine. He may be labeled as an evil person for ordering the death of millions of people, but everything else is simply genius. I admire Hitler for bringing Germany back into a world power, but he can suffer for everything else.
I mean after all Stalin industrialized Russia and made it a superpower. Hitler was on his way of doing so as well. But I'd say Stalin was more a planner than Hitler or Mussolini. Even today Russia is becoming an industrial superpower. It's hard to say, but Stalin had the brains. Hitler and Mussolini relied on propaganda a little too much.
While he didn't live long after World War II, the empire of the U.S.S.R that Stalin helped build lasted for almost 70 years. The empire Hitler attempted to build didn't even last a decade. It's also solid evidence for Stalin being more brilliant by the massive defeat Germany suffered trying to conquer Russia.
Hitler is more infamous, because he exported his particular brand of hate beyond his borders and across an entire continent, and singled out particular groups of people, but the death toll under Stalin was over 3 times as large, granted he had more time to reach it. At the end of the day they're both scumbags.