If you have a awesome Limit Break(s), you get in. If you have an amazing rack, you get in. If you can fight barefisted or an unique way, you get in. If you can heal an entire party and make them invulnerable, you get in.
Tifa, Fang & Lulu sit at the top for many reasons. :P Plus using that Mog or whatever it is to attack is boss. Also riding a Chocobo side saddle is straight classy. Rinoa, Aeris, Lightning, Terra, Quistis are next in line. The last group consists of Sanctum Inquisitrix's and miscellaneous support female characters.
"I live my life 3 videogames at a time. Nothing else matters. Not the mortgage, not my clan and their BS. For those 3 games or less, I'm free."