nobody with the speed and power of Tyson. Ali would have to keep him at a distance with those jabs. Ali's hand speed is much under appreciated though. That would be the fight of all time in my book.
BTW, the most under rated boxer in all this discussion is Lennox Lewis. That guy was the anti-Tyson. That jab of his was unbelievable. Another fight I would have loved to see in the their primes.