In a p4p sense Rocky Marciano MAY be the best heavyweight. But if we're just talking outright, then no.
And this topic becomes more crucial. Now, he has more heart and will to win than even Ali. The elements of his superiority are stacking up to be a clean sweep for everything but handspeed (is that coming soon?) Please to comment further.
His handspeed was underrated too. Remember he only had a 21" reach so his punches had to travel a further distance than any other fighters in history. The fact that he landed punches at all is a minor miracle and that he did to the extent that he did shows that they must have been damn fast to arrive before the other guy could cover up, step out of range, deliver an oration, construct a house...etc.
He is much faster than given credit for. He had quick hands and they found there mark often. Many fast and masterful boxers faced him, and he quite often was faster than them or at least their equal. Marciano is underrated again.
OK. So we have concluded he is the hardest puncher with the best chin, a subtle Yoda-like defense, the greatest output, the best fighting spirit....and now, excellent handspeed. Ladies and Gentlemen, I believe we have the Greatest Of All Time boxers, both heavyweight and Pound for Pound. Case closed. Sport Over.