Um it has to be

Leonard
Hagler
Hearns
Duran

... at least during their era... Leonard did in his prime beat all of them, and Duran lost against all of them I have him last, Hearns beat Duran, and outboxed Leonard, but didn't have the chin so he lost to both Hagler and Leonard. Hagler DID lost to Leonard... he was outpunched, and outboxed... Leonard was more past his prime than Hagler, and Hagler fought a dumb fight which a great shouldn't be doing. As for during their whole career I would have Duran #2 behind Leonard

My top 10 p4p ever not particular order except RJJ
RJJ
PBF
Pernell Whitaker
Leonard
Duran
Prime Tyson
Ray Robinson
Hagler
Ali
Hopkins

runner ups
Toney(when he used to train)
Winky
prime Nunn
Joe Louis
Willie Pep
prime Archie Moore
Aaron Pryor
Liston
Foreman
Holyfield
Hearns
... my list is always changing.