Very stark disparity here. On characters, I think FFXII is about the worst FF on characters of those that actually have characters. All of the characters are either bland and unmemorable, annoying, or Balthier (that last one isn't actually a bad thing but only one character is Balthier). Persona 3, I love pretty much the whole cast, except Ken and Fuuka.

Music - I don't really have a problem with FF12's music, except that I just straight up don't remember it very well. I think it likely strays toward atmospheric. Persona 3 has great, memorable music that I enjoy for it's distinctive style. Again I'm going with P3.

Side Content/Replay Value - FF12 might have more (they both have quite a substantial amount), but I just don't really like it very much. On the other hand, I love the various optional ways to spend time, especially social links, in P3 and how it feeds back into the gameplay. For replay value, I think P3 has some pretty decent replay value, while FF12 barely has play value.

I also have very little doubt I will be disappointed with the way this goes.