Hitman Hearns - Need i say more Julian Jackson... http://www.youtube.com/watch?v=uNXWYM-L2LA speak to Terry Norris, Herol Graham, Agostino Cardamone, ismael negron and 45 other Ko victims.
The TS is not taking P-4-P into consideration in this discussion, so while Hearns and Jackson were massive punchers at the weights they fought at I don't think their straight right hand can be compared to the one possessed by, say, Lennox Lewis.
P4P it has to be Julian Jackson. Anyone thought of Herbie Hide - OK his comp level isn't all that, but 90% isn't bad over 50 fights.
in regards to sonny liston although he had great power in both hands i was always under the impression that sonny's most devastasting punch was the left hook.