I think all of those girls have nice voices but they're too technically perfect. Their voices are all so good that they become boring because there's no character or little flaws that make them interesting. That's why I'd rather listen to someone like Hikki than someone like Celine Dion.

But yes, Hikki does have the best voice in Japanese music, hands down. Then BoA, then Kuu. Namie is not a good vocalist, IMO, and Ayumi is just okay...