The dark destroyer wasn't just a puncher, he was a HELLACIOUS PUNCHER. He literally tried to take your head clear off your shoulders.
My vote goes to Roy Jones. But Dean Francis had very heavy hands, and Henry Wharton had a very robust left hook. Calzaghe was a banger before his hands went.
Hard to measure Benn's power at super-middle, he certainly didn't look as explosive as he did at middle and his punches didn't sound as hard but how much of that was down to the fact he was mostly fighting guys who were coming down from light-heavy/cruiser (whereas he could still make middle comfortably) and how much of that was down to losing speed by weighing more and being older? It's hard to measure.
The power Jones showed against Malinga, Byrd and Thornton was immense and the power he showed a weight up against Griffin and Hill was immense. Leaping shots, -all tendon strength and range of motion in the shoulders. He was also the most relaxed puncher in the world, meaning he conserved and maximized all his strength into the punch impact when he decided to. Awesome puncher at his natural weight, he didn't have a big skeletal frame (skinny wrists).
Tony Thornton also had a really hard punch in his right hand when he landed it right, scored many KOs at middle especially, but had hand operations in the late 80s and again in early 90s.
Reid was a world champion, when is a world champion not world rated? Even after losing the title he was always a top 10 supermiddle for most of his career. He gave Calzaghe a very close fight and would have beat Ottke if not for a corrupt referee and blind judges.
Robin Reid was a great fighter and in this era, would be comparable to guys fighting in the Super Six back in his pomp. I agree, he was never an elite, more a B+ fighter at his best who was always a tough proposition due to endurance, conditioning, power and technique.