I've watch many hwts live. None were as intimidating as prime Foreman. I watched George train in 1972 and saw how he moved vigorously a 300 pound heavy bag with big gloves. Like a plaything to Foreman. Then in the ring sparring with big gloves and watched sparring partners cave with one right hook to the body. Again big gloves. THEN sit and watch him live landing that same punch on opponents wearing 8 oz gloves. I don't know how anyone could take his power for any length of time.
Foreman would be the most frightening, he was a physical behemoth that punched holes in heavy bags. but I think you would feel the most pain against Tyson, the speed and power would result in getting hit multiple times very hard, that Thomas KO was enough to scare anyone, that looks more scary than a one punch KO to me.
Mike Tyson, because Tyson is explosive and as fast as a lightweight, so we can't out-speed him in any way.
Thanks: To make it clear, I'm 100 percent certain that at any point during that 3 minutes he could have ended me. It was light sparring on his part for sure.