As characters, I must go with Squall. Why? His personality is much deeper than that of Tidus's. Tidus is a whiny jock. And sure, jocks can love too. It seems that Tidus has a good heart and everything, which is all nice when said and done, but Squall's personality is much deeper. When playing each game, you obviously have to learn about the characters. With Tidus, you immediately can tell that his personality is that of a stereotype, already. A do-gooder jock who falls in love with the woman who is going to die to save the world. Tragic, yes. But Squall; he starts off battling his nemesis, who ends up becoming an agent of evil very early into the game. Squall seems heartless at first, and obviously is a loner. But why? You have to play the game to actually find out.
Rinoa comes in on a mission, he doesn't expect to fall in love with her, so he doesn't. He tries to push her away, because there's something more to him that makes him not want to get into a relationship with her. Tidus is just full-blown hornball and wants to get closer to her, and he eventually does. There's no fun in that, plus it was hardly as entertaining or rewarding as controlling Squall was. Squall had been an orphan, and his past comes back to him. To haunt, or to confront? Who knows. You still have to keep playing to uncover more about Squall. Even with Tidus, the plot twist that Sin is Jecht, that comes very, very early on. Too early, I think.
X's story might have made more sense to some people, and may be better. VIII's story was a bit confusing, I'll give it that. But this debate isn't about the story, it's about the characters. I think Squall had more to offer, gameplay-wise, and personality-wise. And if they fought, Squall could shoot Tidus before he ripped him to shreads with his gunblade.
Kenshinswife, you offer no argument for Tidus, other than a fangirl's "Ooh, squee, I love Tidus!" Appearence hardly has to do anything with the factor in choosing the better character. But if that's what you're into, Tidus's pants also sucked. They were half-cut on one side, lopsided and uneven. Squall's black attire and gunblade definately makes him look much more badass.