To me Moomba makes the most since. I haven't played II so Beavers are a surprise to me and Wind Drakes are generic like most RPGs out there has some kind of dragon in it. Pupu's look cute but I can't see them being in anything really. Red XIII's species I believe should be unique to VII. His race had more of a central role than the moombas did who were just in a quick scene, so their potential haven't been realized yet unlike the history we have with Nanaki's. I'm bias towards IX so I'd say them even though Moombas are most likely out of anything.