Jaybe nailed it for #1.
Some candidates for #3 (Not the absolute best, but highly under appreciated)
Bonnie Raitt. Listen to Cry Like a Rainstorm by Linda Ronstadt (a clear contender for #2). Then Listen to Bonnie's version. Which conveys more emotion? And her "I Can't Make You Love Me" is a classic.
For technical perfection as a lead and background singer, I think Jennifer Warnes needs more recognition.
Come to think of it, we should do a best background singer thread.