Muhammed Ali definitely.
I'm a tyson fan, but I have to admit Ali would have the advantage. The reason is because despite tysons punching power, Ali proved through previous fights that he could handle it.
This is proven through his fights with earnie shavers, George Foreman. These guys hit harder than tyson, at the very least as hard, yet Ali took the heat.
Therefore, all Ali had to do was to go past 5 rounds with tyson, and pick him apart from there.
Tyson might have been ferocious, but the guy had no stamina, or any willpower past the 5 round mark.
Also, remember it was Ali's speciality to defeat big scary guys like tyson. Apart from the examples I stated before, Ali defeated sonny liston, another tough guy who psyched out his opponents, but Ali still out psyched him and won.
Ali's willpower and toughness was second to none. Even the fighter who gave him most trouble, Joe frazier, lost to him in their final fight. Even fraziers win against Ali in their second fight was not a knockout, it was a long and difficult Road for frazier since he had to go the distance with Ali, something tyson isn't capable of. This was because frazier had more willpower, more stamina than tyson.
Lastly, tyson relied on knocking out opponents to win. If the points I raised above wasn't enough, then you will know that Ali never got knocked out. The guy just wouldn't let anyone win by knockout. He always got up.
Tyson would have to go the distance with Ali, and there's no doubt in my mind that Ali would come on top after it.