I know it's a matter of taste, but I assume we are speaking of a combination of voice, style & appeal? My favorites are from the rock genre, but thanks to my upbringing, I have an appreciation of different kinds of music, and voices. Here goes (in no particular order):
Frank Sinatra
Connie Frances (in her prime anyway. She sang some beautiful Italian songs)
Mario Lanza (I grew up with his voice blaring on Sunday mornings)
Frankie Laine (Don't know why exactly, but I like his voice and style)
Whoever the lead singer in the Platters is (can't remember his name, but his voice was beautiful.)
Rod Stewart
Don Henley
John Lennon
Bob Dylan
Elvis Presley
Billy Joel
I'm leaving so many out, but this is a start anyway.
TIS