I would say Michelle Branch right now. She had two successful solo albums (albeit the second was a bit of a disappointment) and a successful album with the Wreckers.
Vanessa Carlton had a nice debut and a dissapointing second album.
Since Michelle has done more at this point, I would lean towards her. Of course that could all change if Vanessa's next album is fantastic.
I like them both, but I voted for Michelle Branch b/c she has done more than Vanessa Carlton, in my opinion. Yes, "A Thousand Miles" was awesome... but Michelle Branch's singles (Everything, All You Wanted, ...) and collaborations with Santana (The Game of Love and I'm Feeling You) are more significant to me.
