Good recommendations by tablejockey.
It’s interesting that the distinction is being made re “song book” material as concerns both Ella and Billie. The fact is that most of the material recorded by Billie is in fact, and like Ella’s…….also part of the Great American Songbook.
Two different singers with two different styles. Jazz is, stylistically, a lot of different things depending on the particular artist. In fact, individuality of style is one of the. key ingredients of Jazz. Ella’s was not as gritty and pained as was Billie’s. Does that make her less of a Jazz singer? I don’t think so. It’s also interesting that singers seem to be accorded less stylistic latitude than instrumentalists. Was Lester Young less of a Jazz player than Coltrane? After all, he had a beautifully light and smooth tone with perfect intonation (sound familiar?). Coltrane, on the other hand, had tons of grit and angst in his playing and tended to play a little sharp.