It's a little bit of far-stretched to debate on which individual killed more people. If Hitler and Stalin had not kill, others would have. It's the social-political context at the time matters more than a certain "monster".
I don't think it makes much sense to talk about which was worse. And, body count seems like a poor proxy for evil, since it measures opportunity more than intent. If you could objectively measure evil, the winner might be someone we've never even heard of. Still, I'm disappointed to see Stalin doing so poorly in this poll! He starved the Ukraine. He had his own friends imprisoned and executed on false charges. There was no person or population he wasn't willing to victimize to bend the universe to his will. I think we just had a great misfortune to have both these bastards in important places at the same time. And, I wouldn't give him any personal credit for the modernization of Russia, which was something overdue that coming to fruition due to reforms in the late Tsarist era and from the Revolution itself. It's not like he had a great plan for getting it done, or that starving Ukraine, banishing kulaks to Siberia, and murdering half his officer corps somehow created great gains in industrialization.
Yeah, tell me about it... Sincerely, 1939 Poland But seriously, I think a more interesting question would be how would things be different now had Hitler not invaded Russia in 1941. I know war between Germany and Russia was probably inevitable, since that was Hitler's plan all along, but what if they had stuck to their pact and divided up Europe/Asia between them? What if there was no Eastern front to distract Hitler when the Allies invaded Normandy?
I think the US would have to choose between Japan and Germany. I think we could still beat Hitler, but it would have taken all our attention to do it. I was thinking of another, more outlandish hypothetical because of this thread: what if you transplanted Hitler and Stalin, say after the Reichstag Fire, would either have behaved in a different manner than the original? Other than Hitler being upset about running a Slavic empire, I don't know if anything would be different. Stalin in Germany would probably see war as the solution to maximize his power. The Holocaust would probably play out the same. Hitler in the USSR would still have to concentrate on breaking other power structures internally to consolidate his own power. He'd still run the Purges and dekulakization.