Why Sinatra???

Frank Sinatra is like Tom Cruise. I'm tired of that guy being in so many movies. Why is that guy in so many movies? Uh, talent.

His voice and the sound quality here is excellent. Dean is right on the microphone, accompaniment is in the background.
https://store.acousticsounds.com/d/98050/Dean_Martin-Dream_With_Dean_-_The_Intimate_Dean_Martin-Hybr...

I remember dialog from futuristic TV series "Orville":

- There was a contest, long time ago on planet Earth, called American Idol, to find out who sings the best.
- But, why???
- These were dark times.

Each of mentioned singers is so different and some of them like Sinatra are only interpreters while others are composing as well.  Sinatra and Dean Martin are wonderful singers in different flavors.  Enjoy them both instead of comparing.

Unlike Diana Krall, Sinatra gets swing and his timing is impeccable. Probably his most significant talent. Very few get it. Robbie Williams has it too. Swing while your winning is a good effort! Michael Buble just looks cute but never had it and never would have gone anywhere without auto-tune.

Freddie Mercury has it too. I can’t describe this kind of incredible talent. I don’t think it can be taught. I can only recognize it instantly when heard. The gulf between people like Sinatra, Freddie Mercury and others is bigger than the ocean is wide. What you don’t play or say is just as important or more important than what you do play or say.

Viridian....+1 on Sinatra. I never get tired of his voice, a real musical instrument and he was a great musician.  Deano, I like but not much of a musician IMO and Dean tends to sing in a schmaltzy way.

Sinatra was perceived as a serious musician and man, with his Mafia connections and all. Dean had the tipsy comic public image and often sang while in that character, which made people take his singing less seriously. Making movies with Jerry Lewis didn't help either.

I too prefer Sinatra by a wide margin; especially a young Sinatra. Although neither as much as Bennet, but that’s a different story. Sinatra’s phrasing was impeccable and considered by many singers and instrumentalists as “the standard”. The particular quality of their individual voices is a matter of personal taste and although I don’t particularly like the quality of Sinatra’s later in his career his sense of swing as well as phrasing was always pretty great; a true jazz singer. Dino’s voice had an inviting warmth not unlike Bennet’s, while Sinatra (especially later in his career) would sometimes convey for me the sense that he was doing the listener a favor by singing. Ted Gioia does a good of addressing some of this:

https://www.thedailybeast.com/just-how-good-a-singer-was-dean-martin

Not that Deano was a toad or anything but I think the "Betties" were, simply, more smitten with that oh-so-cute face from Hoboken.