This is actually kind of difficult.

1) Auron: Oh Auron, oh AURONNNN. His back story is just awesome and.. well, hes SMURFING AURON
2) Rikku: I liked her character design, and I loved how out of place in the party she was for a while. She was just tagging along for a while and wasnt super welcome, but I liked how that was developed.
3) Wakka (after much thought, I used to hate this guy with such a passion). I hate his hair, but I do enjoy his interactions with Rikku quite a bit. Also I loved his battle with faith. He wanted so hard to believe but the religion he followed just kept stabbing him in the back. It was fascinating.
4) Lulu: Indifferent
5) Kimahri: Indifferent
6) Tidus: Just stop talking please. No, this isn't your story. It's yunas. Get out.
7) Yuna: Oh, you need to be rescued again? Ugh, fine. It may be your story, but you're becoming quite a burden.