I could mention someone legendary, but I will say Sumbu Kalambay. He had the nicest movement and counters I have ever seen.
Duran brawled in such a technically sound and effective way. Louis was great. I don’t like him too much but Mayweather seems to have pretty much perfected his technique.
Off the top of my head: Harold Johnson. Orlando Canizales. Jose Napoles Joe 'Old Bones' Brown Ricardo Lopez Floyd Mayweather Jr Lionel Rose (beautiful technique)
Thomas Hearns SRR Jose Napoles Ezzard Charles George Benton Wilfred Benitez Alexis Arguello Joe Louis I think all these guys and most mentioned so far are technically sound. Joe Louis and Arguello are probably the most "correct" but other guys like SRR were likelier to improvise in there and break the rules a bit, not because they lacked fundamentals but because they were skilled enough to get away with it, and the payoff was worth the risk.
I assume you're asking for guys who excelled with pretty basic, sound fundamentals and textbook technique with no "special effects"--not necessarily the guys who are the most skilled or most complete, right? If so, I might go with Finito Lopez.
Sanchez had many things going for him of course, but he did tend to throw his right a bit like he was throwing a baseball. Had kind of a lever effect thing going on, where he rotated his arm at the elbow. For all he did well that punch always seemed a little awkward.
For all round skills I like Marvin Hagler. He could box, brawl, great jab, great combinations with good power besides being a seamless switch hitter. Add what might be the greatest ever chin then he’s hard to argue against.
I would say Evander Holyfield. He could just about do it all. Had every shot in the book. Jab, crosses, uppercuts and hooks to the head and body and all thrown in nigh perfect form. His only flaw was his willingness and tendency to engage in slug outs when caught which was fine against cruiserweights but risky against the bigger and stronger heavyweights.
