Ali was a great champ and a great boxer, but Norton, Frazier, and Foreman were all a lot stronger, tougher and meaner. Ali was quicker and smarter and better skilled, but the others were all a lot badder. I still wish there could have been an exhibition between him and Teูfilo Stevenson of Cuba, they were both so quick and skilled.
I still get a little spooked when I see any of the Foreman fight tapes. Powerful, cold, mean, and relentless. He was a much heavier hitter than anybody was used to in that era. In one documentary, one of his old sparring partners said that George didn't just have knockout power, he could kill a man with one punch.
In his prime, Mike Tyson was a scary fighter, too. He had a lot of power in both hands. When he went on the offensive, he was vicious. It takes about an hour to watch his first 20 fights because there were so many quick knockouts. It's a miracle that he never killed anyone.