I love the "not till the end, always" quote. It's so romantic even Kimahri smirks at it! And the "I can fly" quote too.
As for the funny ones:
Wakka: I wish I was on a chocobo now..
Lulu: Walk or I'll feed you to one!
(You get that if you cross Mi'hen foot and have both Lulu and Wakka on a battle)
Tidus: I knew you were bad the moment I saw you!
Seymour: Oh ? My sincerest apologies...
(When you battle Seymour Natus, I think)