He is known as the hardest one-punch hitter in history

[Ben Bolt]

Both Muhammad Ali and Larry Holmes said Earnie Shavers was the hardest puncher they ever met.
So, here's a couple of Shavers rights: against Ali at 9:45; and against Holmes, that famous blow at 2:24 (quote: "the hardest punch a man ever got up from to win a fight").

[piojo del norte]

Tyson would make some fools jump around like spaghetti once he hit them.

[alza1988]

Joe Louis

[turbotime]

Julian Jackson

[BigStereotype]

Joe Louis

He was the better (i.e. faster, more accurate, compact) puncher, but as far as sheer impact goes Shavers was much stronger.

[meelimb1]

Paulie mallanaggi

[piojo del norte]

None can hit harder than Big George.

[120]

None can hit harder than Big George.

Ali fought them both, I think his opinion counts

[Forza]

Shavers had average punching power at best

[Ben Bolt]

It's about single-punch power.

For sure, Iron Mike was more devastating, but fighters who faced him said it was his speed that hurt them. They never saw them coming.

For a pound-for-pound choice, Julian Jackson is a good pick.