Perkiness is decided (using the Scientific Nintendo Fan Girl Cute-O-Meter by three factors (cuteness, childishness, and goofy-ness).
Cuteness:
1. Rikku
2. Vanille
3. Selphie
4. Yuffie
childishness:
1. Vanille (who is still a child)
2. Yuffie
3. Selphie
4. Rikku
Goofy-ness:
1. Selphie
2. Vanille
3. Rikku
4. Yuffie
So I guess I gotta go with Vanille. Final (pun intended) answer. But Celestine from Magna Carta 2 out perkies them all!