I don't even think I have a favourite artist. I guess if I made a list of artists, singers or groups where I like pretty much everything they've ever done, it would be limited to INXS (while Michael was still alive), Diana Ross And The Supremes, Eva Cassidy and Julie London. The first two go without saying; they're widely known and popular. Even people who have never heard their music probably know the name.
As for the others, Eva Cassidy's music is thankfully getting less obscure and gaining recognition, but, tragically, she died in 1996 before she ever got to see any of this, so unfortunately it's not like she's going to pull a Tupac and have a string of posthumous hits. Julie London meanwhile was a lounge singer and actress basically, covering the old standards, as you do, and I inevitably end up liking her versions way more than the originals. You may never have heard of her, but she was huge in the fifties; massive star at the time, unfortunately not remembered too well now. Funny how you can go from being ranked Billboard's favorite female vocalist three years running to having no one know who you are in the space of a couple of decades. But yeah; pretty famous.