VII and IX immediately come to mind. But X and XIII also had a lot of character themes....

I'll probably have to go with either IX or XIII. VII just doesn't have the same quanity of quality. Well...I dunno, I was just never a huge fan of Tifa's Barret's or Vincent's Themes but Cid'S Theme, and the amazing rearrangement of it known as "Sending A Dream Into the Universe", gives me pause. As does Aerith's Theme, of course. Sephiroth's too, if we count antagonist themes. Effin' love "Those Chosen by the Planet."

But IX has Freya's Theme, Beatrix's darker boss theme, which I honestly prefer to "Rose of May", Eiko's Theme, Kuja's various themes....

The only themes that really stand out to me from X are Auron's, Seymour's and Yuna's.

XIII had a ton of great themes with Snow, Hope, Vanille and Sazh.

So yeah, IX or XIII for me. Just overall. VII has too meany weak ones. Also Cloud doesn't really have a theme, which is annoying.

As for my absolute favorite? Tough One.

I'll just say Caius' Theme from XIII-2.


P.S.

"Maybe I'm A Lion" is NOT Squall's Theme. I dunno why some people say this.