Quote Originally Posted by f f freak
right okay i was stating my opinion and besides he is a dream. also don't have a go at me for stating my opinion. i think yuna was the leader because she was the one who had to defeat sin for the most part of the game the story revolved around yuna
He's actually an Aeon, really :p.

Anyway, Tidus is not the leader until the end of the story. Sure, you control him, but the game is very linear at the beginning, probably to strengthen the feeling of not being in control. Tidus always has to ask where they are, where they are going, and why they are going there. Doesn't sound like a leader to me.
It is Yuna who decided where to go. She chose to become a summoner and to defeat Sin. That means she decided to visit all the temples. The Guardians (this includes both Tirus and Auron) are just following her, making sure she doesn't die along the way. Sure, Auron is knowledgeable and strong, but he's more like a guide than a leader.

However, as mentioned earlier, the role of being the leader shifts a bit after the Yunalesca event, because an important part in order to accomplish her goal was removed, thus she is not too sure what to do or where to go anymore.