If were leaving rock, I'd consider Joni Mitchell
Great range - and a very good jazz vocalist, to boot. (Also an underrated guitarist).
As a song writer Joni Mitchell is a true genius.She has written at least a half dozen of my all-time favorite songs,including Both Sides Now...which Judy Collins performed so marvelously.But I,unlike many,have never been a huge fan of Joni's *performing style".Different strokes for different folks I guess you could say.