Characters I'd give a slight edge to Persona 3, honestly neither of the games have a particularly great or memorable cast to me but if I had to pick one I'd give an edge to P3, in no small part because of Elizabeth who in spite of not even being a playable character is a bundle of charm none of the other cast members of either game manage to match.

Music is a decent category for both, they got a good spread of both general tracks and standouts, I'd give it to FF XII because I just like its style better.

But replay value finally is where FF XII completely hits this competition out of the park for me, the Zodiac Age version in particular. Between the job system, the insane amounts of ways and routes you can take to tackle the many different challenges available at all kinds of points in the game, things you can craft or pursue way earlier than you're "meant" to, and just generally having a gameplay system that makes running through everything a fun grind, it's one of the primary reasons I like the game so much. Needless to say I've played through different versions of FF XII several times. Persona 3 meanwhile... I can see myself replaying "maybe" at some point. Which is still more than I can say for a few games but it's not even close to FF12. In spite of having played FFXII about 6+ times by now and having only played P3 once, I'm more excited at the prospect of replaying FFXII than P3. On some level I'm sure it's just because I generally enjoy playing the game more, which is true yeah, but I think it's also fair to attribute to the replayability of FFXII as a game specifically.