Wow, this is a long thread, and I admit I've only read about a third of it.
I have a strong background in classical music. For me, the best two female voices today are Marilyn Horne and Anna Netrebko.
But I'm no stick-in-the-mud about classical music. I love pop, rock, jazz, and international.
Other female singers I admire are Linda Ronstadt, Milla Jovovich (yes, the actress/model/musician), Joni Mitchell (brings back memories), Badi Assad, Kate Bush, Grace Slick, the two Fleetwood Mac singers, and many, many, many more... We have a 650+ collection of CDs, and if I tried to list all my fave female singers from all the genres, I'd forget some and do them an injustice.
Chris