Tua. Tyson was the best fighter and overall puncher, but in terms of pure power and brute force, Tua may have been the hardest hitting HW ever.
I like Tua. The other 3 punch devastatingly, face-alteringly hard as well, but they all did a significantly better job of setting up and delivering their knockout shots. People knew it was coming with Tua, and he'd still knock them out. Getting Moorer and Ruiz out of there as fast as he did was spectacular. He takes the edge or me, although I typically cringe in sympathy for the other's KO victims, too.