It was really tough, but I went by which character the game could have done without, and that is Quina.
I thought Vivi was an essential part of the storyline, as well as Zidane of course.
Steiner was a big part of the princess' side of the story, and ended up getting a larger part by disc 2/3....
Freya had a much more interesting, more detailed story than Quina, and while Quina may be a great fighter, I don't think it deserves to beat the character closest to elimination, Freya.