If you're judging power against top fighters , it has to be Manny Pacquiao. He kayoed two p4p guys never knocked out before, Morales and Barrera. He floored Marquez 4 times in 2 fights. He put a serious hurtin' on De la Hoya, who had tasted the power of middleweights. And he just about killed Ricky Hatton, who had warred with full size 147 pounders.
I'd say with his last couple of wins, Abraham has shot up the P4P charts. With his tremendous one-punch power, I'd put him above any of the other super middleweights in the P4P hardest puncher category.
Barrera lost to Junior Jones by KO a few years back. But other than that, that's an impressive list. Although I still feel pure one punch KO power Abraham is ahead of Pacquiao p4p.
It is p4p not heaviest puncher in their weight and p4p he hits way harder than Valuev and the Klits. Also Haye never sparked out any heavyweights he took both out by good timing and hand speed. AA springs to mind, Pac too, Haye when he was at 200lbs was probably P4P the hardest puncher, still up there but not no1, then again if he sparks Valuev out everyone will have him as no1.
Pavlik, Abraham, Maidana - current fighters Mercer has got to be on the list of guys with Earth-shattering punches.
I reckon Valero - his last fight - Pituala (something like that). One moment even fight, the next one right hand and it was over. Second round too.
Square one-punch power? Juan Urango. The reason his KO ratio isn't that high is just because he doesn't get to land square much because he can't cut off the ring well.