These are both games that I've played some of, but not completed. Unfortunately the category of replay value in particular is not really knowable in these circumstances. Nocturne seems to be lacking in characters, so P2 probably has it beat there. On the other hand, Nocturne has better gameplay, which means it probably also has better replay value. Well, I'm stumped. Maybe if I had finished these games I'd know.
Oof this is a tough one, but I'm honestly going to give this Shin Megami Tensei III. While I would agree P2 has the better cast, SMTIII has the better replay value with the boss rush challenges, the Amala Network dungeon, myriad of optional boss battles, two difficulty modes, and collecting all the demons is a challenge. PS has some great content, especially EP which has the better NG+ feature of the duology, but I find it's easier to come back to Nocturne.