Great debate topic. In the end there will never be consensus and even with the same sport often times you must define dominance by era's. I mean you can say Jordan but for his era Wilt dominated more so per se. Or even Bill Russell and his nine rings in 11 years. Tiger is a nice choice for his era [which is of course now over] in golf. Schumi was a nice for his decade of dominance in F1, now its clearly Vettel. Baseball is so subjective and its almost pointless to list anyone. Frankly, by definition of dominance I'd have to say someone like Mo Rivera for his era.
Anyway, great topic.
I luv OTB