Hi... Looking forward to opinions from all  who enjoy vocals.

MY VOTE is for a man who was a pioneer: creative, articulate, with a suave and sophisticated exterior and a voice unheard again to this day; he died far too young - NAT KING COLE
John Kay from SteppenwolfPaul Rodgers from FreeJim MorrisonAll had an excellent voice for their genre imho

Excellent suggestions as above- consider;
Johnny Hartman with John Coltrane
Frank Sinatra 
2nd Note;

On the Pop and Rock side of things;
Rod Stewart is my #1.
Paul Rodgers is my #2

these gentlemen can take any cover and make it their own.

Freddie Mercury. He did rock/pop to perfection. No one did it 'bigger'. He could have sung opera. Anything really. Personally think he is head and shoulders above all the rest

Paul Rodgers is up there in my opinion because he can still do it.

Robert Plant was up there in my opinion but he has lost almost all of his former range.

The real conversation ender is probably Pavoratti but I don't know enough about opera to say. Maybe Caruso but there are no recordings that can actually demonstrate his talent as they are all crude and tinny.
Here is a vote for Van Morrison too but his field was really too narrow to vie for best ever.
Freddie Mercury. Most versatile voice of them all. 

Eddie Vedder. Very unique voice.

And of course Roy Orbison. Magical.
... quite a diverse list so far - THANKS TO ALL CONTRIBUTORS...

Once again: input from audiophile members proves just how diversely (and differently) we comparitivly hear sound LOL!!!
If you leave out about 50 opera singers who could sing far better than any of them and who were male, it is +1 for KURT ELLING !
Sam Cooke and Lou Rawls on "Bring it on Home to Me" are indeed incomparable.
+1  Sam Cooke and Lou Rawls on "Bring it on Home to Me" are indeed incomparable.
Agree with those above.  Also, among the best voice quality, Shawn Phillips. I love his album Second Contribution
Put on some headphones and listen to Robert Johnson sing Dead Shrimp Blues..  Wow

Always was partial to some early sides from Luther Allison.  Really great voice.  Check out the stuff from the Ann Arbor Blues Festival.

Easy one: Sinatra
Absolutely perfect tuning
Full control on his voice, can make it sound velvety or harsh
And what really sets him apart: phrasing, to die for, up there with the best jazz player ever
john421, George Michael was such a pop figure that I think he often gets overlooked in regard to his voice. I was never a big fan and I'm still not but I do own Freedom '90 almost entirely because of how big and soulful his voice is.
Sinatra excluded there is only one Joe Cocker at the Fillmore East.

Someone wants to hear the real pavarotti. Look for la Bohéme with pavarotti and Freni. Decca. Best opera recording ever. Not without faults but the live feeling...and the voices!
While I wouldn’t consider him to be "best ever," IMO Jay Black (often referred to as "The Voice") definitely deserves mention in this conversation.

And that would apply even when he was 72+ years old:

Also, the late British singer Matt Monro (sometimes referred to as "the British Frank Sinatra") deserves mention IMO.

In saying all of this, I am assuming the thread is not intended to encompass opera and classical singers.

-- Al
Freddie Mercury
Paul Rodgers
Steve Walsh(pre 1982)
Steve Perry
Joe Cocker

Nat King Cole
Dean Martin
Bing Crosby
So far:

Freddie Mercury-5
Paul Rodgers - 5
Nat King Cole- 3
Frank Sinatra-3
Sam Cooke-3
Good call, Gary (Gsm18439).  Without contradicting what I said in my previous post, I'll second Paul Robeson.

Best regards,
-- Al
Sinatra for sure. Tony Bennett. Gordon Lightfoot, Paul McCartney, Elton John, Van Morrison, Marc Cohn, Bruce Hornsby--no one should try to sound like any of these guys---can’t be done. Maybe a Beatles tribute band, ok.
In his prime, Ray Charles was amazing. Nat King Cole, who early in his career was known more for his piano chops, is and always will be an iconic vocalist. Bobby Darin was a hell of a singer, with a swagger that has rarely been matched since his all too short career ended at the age of 37. Last, but not least is the Master, the Voice, the Chairman of the Board, Old Blue Eyes himself - Francis Albert Sinatra. He did it his way, and nobody has ever done it better. Sinatra didn't just sing a song... he interpreted it with impeccable phrasing, he made you feel as if he had experienced whatever the lyrics conveyed (because he had!), and his natural ability as a fine actor gave him a stage presence and lent an ambience that his contemporaries could never equal. He made you feel like he was singing to you, and that whatever happiness or sorrow you may have encountered in life, he had been through it too, all too many times. Who else could sing of lamentations, heartbreak and being down and out in a way that was, and still is so totally relatable. One listen to the classic Sinatra album - Sinatra sings for "Only The Lonely"- is all that's needed to convince most anybody that Sinatra was in a class by himself.
This is indeed a diverse list.  Given some of the nominees, I am a little surprised there are no votes for Bob Dylan or Neil Young.  :)
Howlin' Wolf is the Greatest Male Vocalist of All Time.

Honorable Mentions:

Scott Morgan.

Gerry Roslie.

Mitch Ryder.

Joey Ramone.

Iggy Pop.

Otis Redding.

Al Green.

John Kay.

Steve Marriott.

Paul Rodgers.

Gene Clark.

Jay Farrar.

John Fogarty.

Little Richard.

Barrence Whitfield.

Burton Cummings.

Mark Lanegan.

Rob Tyner.

Scott Walker.

Charles Thompson 1V (Black Francis/Frank Black).

Roy Orbison.

Roger Daltrey.

Jack Bruce.

Johnny Cash.

Glen Campbell.

Alex Chilton.

Chris Farlowe.

Jimmy Reed.

Arthur Lee.

Roky Erickson.

Eddie Cochran.

Richard Thompson.

Johnny Burnette.

Big Joe Turner.

Sam Cooke.

Smokey Robinson.

Ian Gillan.

Ronnie James Dio.

Wilson Pickett.

Carl Wilson.

Muddy Waters.

Greg Allman.

Stevie Winwood.

Levon Helm.

Richard Manuel.

Layne Staley.

Chris Cornell.

Bobby "Blue" Bland.

James Brown.

Sam Moore.

Clyde McPhatter.

How about Louis Armstrong's vocal performance on "Ella and Louis"? Gotta love it!