For bar room brawls here's my list

Alive and in fighting shape
Vitali
Wlad
Mayorga
Tua
Pacquiao (he's tiny but I wouldn't doubt he could whip any big dude's ass)

All-Time
JOHN L. SULLIVAN
George Foreman
Jim Corbett
Jack Dempsey
Tex Cobb
Roberto Duran
Sonny Liston