I do agree with Flower that XII is quite underrated, the gameplay is excellent with some stand out characters but I'm not mad on the story. However Yuna is a much more interesting character than Ashe, for a variety of reasons. Ashe irritates me with her "well I'm a princess so everyone should do as I say because I am so great" attitude, despite the fact she has only ever succeeded due to other people. Other than that she just isn't very interesting.
Yuna had much more depth as a character I found, conflicted between doing the right thing to help everyone else and her own fears. She also had no problem getting things done, and put others ahead of herself. The polar opposite of Ashe getting nothing done, and seeing herself as the most important.
Yuna gets my vote, but that's because I'm ignoring X-2.
One thing I will always like about XII is how much more real the characters felt but, at the same time, I wasn't too fond of Ashe. Yuna was pretty cool. It was an interesting take on the whole Summoner thing. I always thought that her happiness was always forced, but I guess that was kinda the point though, and it was a trait that I liked. It takes a lot to put on a brave face and keep going despite how hopeless a situation may seem. Just... don't get me started on X-2. That just wasn't Yuna, okay?