Its difficult for me to say who was the best of all time. You really have to seperate it into time periods. Different tactics different weapons...etc.
However, if I had to choose the best of all time, I'd say Alexander.
As for, WW II, its way overrated. There were no military lessons learned from that war, all the Allied Generals were idiots. If military superiority settled things, the Germans and Japanese would have won because they were by far, and I mean by FAR, the best soldiers.
No one has mentioned Scipio Africanus. He's certainly up there. Arm chair?