Bob Dylan 'cause he can hold his breath the longest. Well he said it not me.
Well seriously, depends on what you are looking for, voices have different qualities, singers change with age (and addictions I guess...) the best singer soul for soul, Otis Redding, neatest package (phrasing, musicality, zest), Frank Sinatra, the best blues voice, Muddy Waters, best tone, Brook Benton, most interesting timbre, Nat King Cole, Johnny Mathis, Al Hibbler, and the list goes on. Geez! I guess I'm off the topic again, we were playing "best of", oh well seems I don't like that game anyway.