Joe louis could knock you out from 6inches by using leverage and technique but dont think he could compare to the much larger heavyweights of the later century. Foreman and shavers were monsters they were definitley the pinnacle of heavyweight punchers. I think lennox lewis has a shout to be in the top 5 that right hand over the top was devastating. Tua looks pretty devastating in his highlights also.
Rarely hear mention of Curtis Shepperd but a recent article posted here quoted Archie Moore rating him as a harder hitter than Marciano ..
Marciano, underated due to size may have hit hardest, Joe louis and Dempsey also. Foreman, but he needed very easy target. Getting into position to land is very important, Tyson was great at it. Those four are my top picks. Shavers and Tua are most overated
For one shot,,,,,, Jeff 'Candy Slim' Merritt For one punch, his left hook may have been the single-most devastating shot.
Joe wasn't the hardest punching heavyweight, but his left hook was lethal. Most fans who know the sport will tell you that. Still a hard puncher acknowledged by many of his opponents. Single shot one punch power goes to Shavers, Baer and perhaps Fitz. Most power in both hands combined, George Foreman is #1, followed by Liston and Tyson.
It's hard to say / tell............ However, I will say the right hand Lewis bounced off Ruddock's jaw in round 1 back in '92 was as wicked as they come....... bbb MR.BILL:hat