I think Ali would win. However I think Tyson would have a very good chance. He was untouchable until he got involved with Don King and lost his trainer Cus D'Amato. After That is when he went down hill, the partying, the technique got sloppy and all he did was try to power his way through fights; his defense declined terribly. But both in their prime would be a amazing fight too bad it couldn't happen.