Julio Cesar Chavez is my pick. He fought everybody.

Roger Mayweather
Meldric Taylor
Pernell Whitaker
Oscar de la Hoya
Hector Camacho
Kostya Tszyu

no he didn't beat them all, but he fought them all

108-6-2 (87 KOs)
in a 25 year career.

In his prime he wasn't the best at anything, but he was really good at everything.