I prefer Christine McVie to Stevie.
They were both great in my opinion.
I have come to value Christine‘s voice over Nick’s, Christine has a very pure, polished sound. I have been listening to Nicks since her 1st album, Buckingham & Nicks, her song writing skills have always been great.
Another vote for Christie and also Ann Wilson. Stevie when she stays with songs she can actually sing is good, when she tries to push the envelope—nope.