I agree with FTF, I do not think there was any particular "leader". Everyone pretty much worked together in the story. If I had to pick a character with the most leadership qualities, I would pick Auron.... but that's just me.

I do not dislike Tidus either. Yeah he is pretty feminine, and yeah he is a touch on the whiney side... but so what. Then again I don't dislike a lot of people. I really didn't even notice how whiney he actually was until I saw how frequently other people commented on it. Then when I replayed the game, I noticed.