The two most beautiful Jazz voices I’ve heard.
Vaughan
Wilson
Thirty years apart, they did different songs, but who is the best?
Either
Ella Fitzgerald or many years later Melody Gardot.
Vaughn. What do I win? 
I have total respect for Cassandra. But Sarah Vaughn is…Sarah Vaughn.
When I was younger and trying to make sense of the Big 3 girl jazz singers, I figured that Billie Holiday sang from deep inside the lyric, Ella sang/glided/flew on top of the lyric and Sarah Vaughn integrated both qualities. Generalizations that don’t stand up to scrutiny, to be sure, but Vaughn’s ability to “sit in the middle” and deliver a lyric with style and substance was beautiful…
My undying gratitude.
Ella surely can scat.
Or better yet, the version where she forgets the words. This is pure Ella, and can’t be touched.
Oh, and the OP? Sarah Vaughan, of course.
Yeah, I love that.
Vaughn, hands down