I think Hitler blew it more than anyone else won it. Hitler really didn't need to declare war on America and he really didn't need to invade Russia at the point he did. He had a peace treaty drawn up and the Soviets were really not ready for war as the initial results proved. Russia was not a serious threat to Germany at the time. Hitler seemed like such an impatient man and in such a hurry to carry out his mental ambitions and as a consequence it was too much too soon and all the elements he was raging against joined together and as a team picked him apart.

There are different ways of measuring who won, but I don't think it really matters as every ally played a significant role. The Brits were the first to mount a meaningful resistance, the Russians sacrificed tens of millions, and America was able to kick start its military industrial complex.

The lesson learned from the Hitler experience was that you need to dominate in a different way to that employed by Hitler. No less extreme, but to carefully pinpoint where you will invade, apply economic force, pretend that you are the good guy. In reality it is just a more subtle version of fascism.