Nicks or McVie.....

Stevie Nicks, a goat?  You guys haven't heard Shakira, have you??

"Its funny to read all the negative comments about one of the most beautiful singers of a generation"

Nicks fans always highlight her sexiness and looks.  Her evident pitch problems are the main reason I don't find her singing appealing. . . 
In the end, everyone's looks fade. I thought we were talking about vocal abilities, here.   

Both are great, McVie obviously less celebrated.

IMHO no one can match Linda Ronstadt's energy, quality and excellence in different types of songs and music. Not a bad looker either....I regret never having seen her live and really am sorry she has gotten ill and not been able to perform in a long time. But she recently one a big Kennedy Center award, so someone must agree with me.

That's singers only of course.....she never wrote much if anything.

Linda Ronstadt, for sure.

"IMHO no one can match Linda Ronstadt's energy, quality and excellence in different types of songs and music".

I can think of a few others who, to my ears, are just as excellent in their own way (Emmy Lou Harris, Tracy Nelson, Judy Collins, Linda Thompson spring to mind immediately) but you are certainly right about L. R.'s quality and consistency spanning multiple genres. In that regard, she has no peers.