RJJ is the most likely candidate and probably a greater physical talent than either PBF and Pac, but unfortunately he fought at a time of relatively low-level competition. Its no fault of his but to be among the greatest you need fellow greats...like Ali with liston, frazier, foreman, etc. And against the best available, ie Hopkins and Toney, he produced unremarkable performances...though he clearly won. I also deduct points for PEDs.

PBF and Pac have put on great performances against the best available, like ODLH and Hatton. I think you have to go back to Sweet Pea, who is easy to compare with PBF, for an equal. He had great completion--Chavez and Nelson and McGirt--and performed in a great manner when he fought them. He almost beat a red-hot prime ODLH too, when he (Sweat Pea) was already in decline.

Its much harder to compare Sweat Pea with PacMan, Apples and Oranges and all that. JCC was a similar fighter though, but I think Pac is clearly superior. Duran would make an interesting case however. Similar furious style and a great defensive fighter too, with a lot of head movement. While it appears Pac is more dominant than Duran was at the higher divisions, Duran did fight better competition...defeating the great SRL at welter and facing monsters like Hagler and Hearns.