I also like this archetype. Vanille, Selphie and Rikku are characters I always enjoyed having around (if only they suited my playing style I'd have used them even more). I don't feel Penelo fits the type, and I actually found Yuffie and Eiko a little annoying. I think Eiko is a bit young to fit the type, too, though.

For me it's more about how upbeat they are and how carefree they are. Yuffie could be quite negative compared to the likes of Rikku and Vanille. Or maybe that's just the way I felt at the time. Hard to say!

I feel it's important for FF games to have these kind of characters. Quite often the mood is low and you need someone like these girls (the closest to it for a guy would probably be... Vaan? Gau?) to motivate the party... and the player.