Top-5 hardest punchers at HW division (on the top level)

Utter speculation! I could say Cunningham's knockdown over Fury was more impressive than Wilder's knockdown over Fury (since Cunningham did it with a single punch as opposed to Wilder's combination that put Fury down).

Whyte knocked out a durable Dereck Chisora and never previously KO'ed Lucas Browne. For me, those are far more impressive displays of power than any of Wilder's knockouts.

Povetkin starched a guy named Duhaupas who Wilder could not even drop after 11 rounds of flush, maximum powered punches.

Anthony Joshua himself knocked out a durable Dillian Whyte who had never been knocked out by anybody else, before or after and that knockout from Joshua over Whyte > any of Wilder's knockouts.

 

Joshua #1, hands down.

Then simply the rest in any order.