What are the top ten greatest fantasy fights of all time? Who would win and why?

I was wondering what are the top ten greatest boxing bouts that never happened, such as Joe Louis vs Ali or a Leonard/Hagler rematch, and who would win and why? Whould Ernie Shavers at his best beat a prime George Foreman? Would Joe Louis at his best beat Ali? What about Rocky Marciano? Could Willie Pep have beaten Sugar Ray Robinson when they were in their primes? If you can, please give fact-based answers.