Mahalia Jackson Patsy Cline Whitney Houston Annie Lennox Adele Alicia Keys Kelly Clarkson Christina Aguilera Enya [voice of an Angel]
I'm an Ella fan, but my favorite female vocalist is Doris Day. Patsy Cline was great, and so is Alison Krauss. I also like Norah Jones & Helen Merrill and lots of others.
She right up there with the best with a voice that's as clear as a bell. Wish she had done more original material and fewer "remakes" though...
There's no one greatest it's all subjective If I had to name one it would be Karen Carpenter Love these gals too Barbra Streisand Kate Bush Enya and the amazing Alison Moyet
Yesterday, I received the shock of hearing Françoise Ogéas in the lead role (l'Enfant) of Ravel's lyrical fantasy work "L'enfant et les sortilèges", in the version below. Good grief, was she sped-up?!.. This is purely from a technical viewpoint - as the OP's thread title suggests - as I do find her vocal color out-of-date and a little irritating... But such pitch accuracy (on demanding intervals) and upward range... Wow!!!
Sandy Denny was the first singer I thought of, though there have been many excellent female singers in the history of music who deserve mention too.