I've yet to finish a single "Persona" title, but I love and have played Nocturne and Digital Devil Saga. If I were to start playing Persona games, which I will at some point, I'm starting with the first two. Atmosphere/mood/setting-wise, they are way more appealing to me. I have nothing against P3 & P4, I've actually played both for a decent amount of time back when they launched on PS2, but they are WAY TOO high school kid problems for my taste, lol! They're cool games and everything and they do a lot of neat things with their battle systems and such, but there's way too much of a focus on teenager drama, dating, and after school activities. No thanks.
I know people are going to take this the wrong way, but I've always thought of Persona as games for people who haven't moved on from high school. A lot of people I've met in life always reflect back to high school and it amazes me. I fucking hated high school. My best memories are from my college years, but you never see people reflect on those times, at least not the people I've met/worked with. I guess that's why the Persona games are so popular, right? From observations (or for more or less shits and giggles) I assigned the SMT games to particular stages of life:
Persona: For people who are still in high school or can't move on from high school.
Digital Devil Saga: For college students or generally people pursuing a higher education.
Mainline SMT/Nocturne: For adults who work full time jobs and have little to look forward to other than survival and paying bills. That's at least where I find myself now, lol!
Philosophical mama-drama aside, SMT: IV's gonna be hot!