As for who killed most - If you attribute the 50 million deaths of WWII directly to Hitler (after all, popular opinion dictates that there would have been no "world war" had it not been for his and Germany's agression, at least not on the scale that resulted), then Hitler is probably ahead by 20 million or so.
But then we really don't know how many Stalin is responsible for, do we. Estimates put it at 30 million, but who really knows.
As for Hitler being 'Intelligent' - I doubt he actually was of more than average intelligence. He certainly had a gift for oratory, and he also had a knack for getting to the heart of the people's 'pet peeves'. It's these skills that he used to 'fool' and 'rile' the German people (who didn't need alot of persuading anyway), that allowed for his rise. The Allies total blindness and apathy regarding the state of the German economy and other socio-economic consequences of Verseilles would have to be counted among one of the main reasons for WWII coming about.
Many (before me) have said that WWII was a direct result of the stupdity of WWI. Just a different type of stupidity. Period.
The tactics that won the campaigns in Polland, The Lowlands and France were due to mainly the 'Blitzkreig' philosophy, which was not Hitlers at all. The great Tank commanders, such as Rommel and Guderian were responsible for speed of those victories, and Hitler knew it. Along with the rest of Europe's 'lack of stomach' for war.
No, not a genius by any stretch. Talented, yes. His biggest problem was that he actually thought he was right!!
As someone pointed out earlier, the mans evil leanings and his 'unreasonable' and 'unfounded' ideas about race and superiority were well documented when he was a nobody. So he was always going to be 'trouble' ;D
