Cassius Clay AKA Muhammmad Ali and it isnt even close.
Reason why??
Ali would do everything possible to get inside Tysons fragile psyche.
Ali had superior footwork. Tyson would stalk Ali and miss leaving him open to Ali's counter punching. Ali had an iron jaw, Tyson never had anyone hit him hard.
Tyson relied on intimidation, Ali would not allow himself to get intimidated.
Foreman would have destroyed Tyson as well.
End of debate.