Don't know how I wandered into a "best" thread, ah me. As the wide range of opinions flood in, it's obvious there are many criterion to go by. I never would have thought of Jim Reeves, but he definately had a sonorous voice, further underscoring just how subjective this "best" thing is. The best Van Morrison is a very moving listen.
I saw the film ELIZABETH the other day. It struck me that as important as most of those historical figures were to their own times, it would shock them all to know (save Elizabeth herself) that 400 years hence they've been largely forgotten, with most of their trials, tribulations, as well as accomplishments, relegated, at best, to the historical trivia bin, and dwarfed, DWARFED, by a writer (a writer??) breathing the same 1600 air as they, yet most of them probably never even heard of him: William Shakespeare.
It's hard to predict who will survive the 20th century as a household name in the 23rd century. Not many, that's for certain. And probably few of them could be accurately predicted here. Maybe even Hank Williams! (sorry for the "even," Hank, you know I know how great you were) I tell you, with the miniscule hindsight of just 30 years, it's hard to imagine the Beatles not bestriding the 20th Century like a colossus--rarely has art and popular acceptance converged as it did during that 7 year recording span. And, McCartney, if you want to be technical, had a great (and evocative) range.
On the other hand, in terms of influence, a defining of the times, just sheer name-that-voice-in-5-seconds, as well as that special something, you can't ignore Elvis Presley in this "greatest male singer of the 20th century." Somehow I think this tag goes beyond simple octaves. In fact, though I haven't read a lot of this thread, those posts I have read, in not mentioning him, struck me as taking pains NOT TO, as certainly every man-on-the-street interview we'd like to conduct would invariably offer up Elvis in seconds.