For Blitz Ace itself, the only variables seem to be who pitches and what happens if Tidus connects with the blitzball or not.

As for the game, you see different scenes in a few places depending on who gets the highest affection rating.

But the overall plot is the same no matter what. The (SPOILER) Macalania pool scene has to take place with Yuna. Maybe that's just as well. Imagining it with Lulu is kind of scary.