Tough choice...

Faye Wong has a pleasant, rich voice and is a very skilled singer. Same goes for Emiko Shiratori. Rikki, as a folk singer, is naturally different to those two - she's got a remarkable vocal range, even if she gets a little whiny on the very high notes. But then, that's hardly bad; it's just an aspect of her style.

I'd have to agree with crono_logical. Risa Ohki is pretty glorious, in any of the languages she uses in the FF Vocal Collections. However, since those are arrangements, not actually from the games themselves, are they valid for this poll?