I like the CD Only and the regular CD+DVD covers. In ther Pouch cover she looks too much like Ayu to me and I don't like it at all.
But anyway, the covers are at least slightly different and I think it makes it easier for fans to buy these. For me the best cover is the regular CD+DVD. Kuu looks cool. :3
Btw, what's this talk about Kuu having a ball with her in the cover again? I think I've missed something because I haven't seen pics of Kuu holding a ball so much. o.O