I have an idea! Let's take the weakest characters from XII and pit them against the "weakest" (let's face it, even the weakest aren't that weak) characters from IX.

From IX we have Garnet, Vivi, and Eiko.
From XII we have Penelo, Fran, and Vaan.
(These are just my opinions, don't get pissy)

XII's characters go in guns blazing, little red lines coming out and connecting to their victims, thinking these little cartoons are goin' down, "BUT WAIT!"... what's this? Vivi's unleashes Firaga and Vaan is reduced to Ashe, lol. And what is that in the sky? Oh my gawd it's Garnet's Bahamut! Even the weakest most lame IX character, Eiko, is bustin' out with Fenrir. Penelo runs for her life but gets cut down in a burst of dragon fire, while Fran is being used as a doggy chew-toy.
XII's weakest characters are decimated.

So, Voltron, I choose IX! XII was fun but undeserving of an FF title.