On the 100th anniversary Frank Sinatra's birthday, I would say that Sinatra sang with the most ease of any singer I've ever heard. He truly was the smoothest of all. There is a power in his voice that is not the product of a visible straining that is discernible in even the best singers. No one did it with as little seeming effort as Frank Sinatra.
Which isn't to say it's not there. Rather it is all very seamless. No missed notes, no vein popping exertion and of course great material from only the best songwriters.
A good example is Fly Me to the Moon wherein a deceptively loose jazzy band jousts in a friendly way with Sinatra has he rides them home with unexpectedly powerful moments of vocalizing.
But one can't Talk about Sinatra without addressing his pop culture persona - The violence, consorting with mafia figures, the love affairs etc. The image perpetuated by shows like Saturday Night Live of an angry, vain Sinatra.
Well I prefer to listen to the music and separate that from papparazzi. If you want to say something positive about Sinatra other than about his music, look at his history in regards to civil right sand standing up to racism. He was well ahead of the curve there forcing Las Vegas to desegregate their hotels for entertainers who performed with him such as Sammy Davis Jr and Lena Horne who could perform at a place like The Sands but had to go to a hotel reserved for black people to sleep. This was a time, even after black entertainers could sleep in the same hotels, when a swimming pool would be drained after Davis had swum in it or all the sheets and pillowcases burned after Horne had slept on them.
And then there's this http://time.com/3857736/frank-sinatra-civil-rights/
Of course Sinatra did later perform at Sun City in apartheid era South Africa and backed Ronald Reagan but he was the type of person who took things personally and he never got over the snub of JFK after helping him campaign for the presidency in 1960.
Frank Sinatra was a complicated public figure who also made a few great films not THE MANCHURIAN CANDIDATE and FROM HERE TO ETERNITY but also THE MAN WITH THE GOLDEN ARM and the criminally ignored SUDDENLY pulled from distribution after its too close parallel with the assassination of JFK.
Ignore the caricature, listen to the records, appreciate the voice of a master.