By the way, if we're talking voice, it's important to appreciate the human voice as a performance instrument and not a note-producing machine. Singing is much more than hitting a note and pressing on it with power. That's a demonstration of technical skill, good for audience reactions on America's Got Talent and a nice way to end a ballad, but mostly irrelevant in music.
Think of your favourite singer singing your favourite song; the magical moments feature a phrasing, a feeling, a timbre, a stretch or strain, something unique to their instrument. You're hearing a performance. What makes it great isn't them sitting on a note and applying vibrato for 15 seconds. Power and vibrato will help you win a talent contest, but that's not what makes a great song.
Which is a long way of saying I have no idea how to choose my favourite male singer, because there are way too many of them with way too many unique styles. Stevie Wonder, Smokey Robinson, and David Ruffin (The Temptations) are all classic Motown singers, but they're as different as a cello, a piano, and a trumpet. Three great instruments with three entirely different sounds.
Paul McCartney had an amazing pop voice – he could do rock and beautiful ballads equally well. He's an all-time great in his particular musical lane. So is Sting, for similar reasons. Neither were virtuoso singers, but both knew how to use their vocal instrument to perform great songs of their particular genre.
Other great vocal instruments: James Taylor, Otis Redding, Al Green, a dozen more I'll remember five minutes after posting this...
Oh - and what about Crosby, Stills & Nash and The Beach Boys? As a longtime harmony guy, I have to give a nod to collective singing, which is a whole other level of vocal precision-flying. Singing is a blast, but you haven't lived until you've sung in a choral blend.