guys who always showed up and never underestimated their opponents. They didn't necessarily win 100% of their fights but guys who were nonetheless consummate professions. Hopkins and Usyk come to mind. Edit: I am going to add Dimitry Bivol, Floyd Mayweather Jr, Andre Ward, Salvador Sanchez, Marvin Hagler, Rocky Marciano to the list based on some of the posts below.
Povetkin Quarry Come to mind for contenders. They had long successful careers because they were always ready at every stage of their career.
Mayweather, Joe Frazier, Usyk. I'd probably give Usyk first place actually. He is always 100% on it, his concentration levels and dedication on and off the ring is unbelievable.
Quarry? He had a penchant for coming into fights undertrained and injured, didn't he? He was game in the ring but oft flabby and carrying injuries.
After thinking about it would have preferred to use Patterson. Quarry was always game. Which may be a bit different than always ready. It just didn’t cost him maybe as much as others.
In his title reign, sure. But he appeared complacent when he fought Sanders. He might have been in good shape for Sanders but mentally he didn't seem to have taken Sanders seriously.