Erm... How exactly do we measure this? Tyson could probably outdo Lewis in standard gym tests, but he got muscled around the ring like a rag doll. It could have been a heavyweight who sucked major balls. Didn't Marius Pudzianowski box at some point?
IN the weight room Louis Monaco,Hasim Rahman,Shannon Briggs IN the Ring imposing their strength Foreman(especially the old one) Vitali
Probably a prime Holyfield. Prime Holyfield was legit and was as strong as a 300lb fighter. He overpowered Foreman. Michael Moorer was pretty damn strong too despite his chin, and what about David Tua? Or Ike Ibeabuchi? Either Holyfield or Ike take the #1 spot as strongest boxer pound for pound. There is a difference between being big and being strong, being strong has more to do with having good genetics and the right kind of muscle fibers. Valuav, Vitali, these guys are big but they aren't strong for their size because if you look at their bodytypes they aren't built to be strong, if you look at the bodytype of a Holyfield or an Ibeabuchi these guys are built to be strong and probably could benchpress more than guys twice their size.
Or Tyson would have been my choices. Foreman was a giant among men, and Tyson was as strong as a giant for a smaller man.