The definitive version is definitely Persona 3 FES since it's 2 games in 1 -- The Journey & The Answer. To be honest, The Journey is the main attraction since there's new quests, social links, demons, weapons, and the best part...visual attire! The original Persona 3 had you customizing your party's attire but with no visual difference. It used to drive me nuts not seeing what the girls were blushing about when I gave them a certain attire to wear. But yes, The Journey is the best part of Persona 3 FES and The Answer is more of a side quest than a additional sequel. You're stuck in the dorms until you've reached the top...*SPOILERS*...kidding. There's a story but you'll be too busy just trying to stay alive. It's challenging but fun. I highly recommend both Persona 3 FES (PS2) and Persona 3 Portable (PSP).