My faves...

Funny:
WoL Vs Shantotto: This is blood lust is simply not normal
Garland Vs Cloud: My sword can crush yours in turn!
Firion Vs Firion: I will even best myself!
Firion Vs Bartz: So, are you flashy when you play?
Onion Knight Vs Firion: Don't you think you have too many weapons?
Onion Knight Vs Cloud: If you keep worrying, how do you make progress?
Onion Knight Vs Squall: That is such a cool weapon
Onion Knight Vs Garland: Don't brag just because you're bigger!
CoD Vs Shantotto: The same... no, this is something more...
Cecil Vs Zidane: If it is with you, our fight shal be cheerful.
Bartz... screw it, they are all awesome

Exdeath Vs Onion: You look so tiny.
Terra Vs Bartz: Can't you be serious?
Most of Kefka's are awesome as well but the on for Tidus and...

Kefka Vs Kefka: Let's go, you lady killer
... stand out the most.

Squall Vs Onion: I don't like kids.
Its official, I am the real life Squall

Ultemacia Vs Kuja: At least you fight with proper etiquette
Zidane...
Vs Terra: A girl? I don't think I can do this...
Vs Cloud: Wouldn't you be more popular if you were just more cheerful?
Vs Squall: If I win, I get your weapon!
Vs Shantotto: If I win, can we go on a date?