I guess it's got to be Colleen (from Big Blood/Fire on Fire/Cerberus Shoal)
But I gotta give some honourable mentions to Jenny Hval and Bianca Casady from CocoRosie and Dawn McCarthy and Robbie Basho and Gareth Liddiard and Glen Hansard and I should probably stop now or I'll just keep on going
I strongly approve of these choices
Robert Pollard, with Neil Young as a close second.
Karen Dalton, super underrated on here and a great guitarist too. Bob Dylan's favourite voice too