Criterion: they have had to have held the boxing championship at some point during that period:
(TOP 5 IN ORDER)
Post 2000
(1) W Kiltschko
(2) L Lewis
(3) A Kiltschko
(4) David Hayes
(5) Valuev (maybe but included for interests sake)
70's & 80's
(1) Ali
(2) Holmes
(3) Norton
(4) Tyson
(5) Foreman