I think Abraham is p4p the strongest fighter in boxing, I don't know if he's the hardest hitting though.
Juan Urango. He'll always have his weaknesses because he doesn't set up punches, and he needs to set his feet before he throws, but when he lands clean, it's pretty much lights out. The Vilches KO was sick, he broke Ngodjo's jaw with one punch.
Juanma or Abraham. Juanma's knocked some guys with sturdy chins clean out. Abraham was a beast of a puncher at 160 so imagine him at 168.
I don't agree with JuanMa, he KO's guys with multiple landed punches, he doesn't have one punch KO power. Look at his fight with Ponce De Leon, he was able to land at will, he never took him out with one punch it was with repeated hooks.