After reading through this entire thread.....
How is it nobody recognizes Francoise Hardy?
No mention of Bessie Smith, unbelievable..... Kids
The best I've ever heard ... live only...
1. Emmylou Harris
2. k. d. Lang
3. Joan Armatrading (don't think she's even been mentioned, was killer back in the day)
Honorable mention to Linda Rondstadt
Over rated mention to Grace and the singing goat (Nicks)
The thing about Emmylou is perfection. Lead, accompaniment, or backup, she nails it all with her uncanny sense of tone and vocal precision.
The ultimate professional, not many can do it.
It's why after 40 years they all still stand in line to record with her, even though the voice is way past it's prime.
that's grace slick, Not the nocturnals