Frankly, Garnet is the only good pick of the bunch. Aeris was a flirty schoolgirl, Rinoa was bland and Yuna was aggrivating. Garnet was the only one that had depth to her character besides the love story between herself and the hero.

Aeris: 95% of her purpose in the game was to create a love-triangle between herself, Cloud and Tifa. The other 5% was the whole "summoning Holy" thing.

Rinoa: absolutely no reason for being in the game besides the love story with Squall.

Yuna: she can summon things. And exactly how useful did that turn out to be in the overall plot of the game? If I remember correctly, her whole "quest" was a sham, wasn't it? Yeah, she was only there for Tidus to swoon over.

Garnet wins.