I don't like Selphie, there's absolutely nothing good about her IMO. Quistis has some good stuff though like Degenerator (cheapest move in the game, makes it sooo easy to level up if you want to), Big Guard (I think that's the name.. it's sort of like the one in FF7, not entirely though) and Shockwave Pulsar (only spell that can do more than 10,000 damage). I don't like Rinoa too much battle-wise, so I'd say Quistis is my favourite in battle amongst the girls. Story-and-other-than-battle-wise I'm not sure..