I say Devil Summoner 2. You're already at the final boss so go for it. The final area, the bottom level of the well, and the first games final dungeon give about the same experience. My favorite place to grind was the first games final dungeon (as you can tell I can't remember the name xD). The battles are time at two minutes and there is no negotiating. So you can fight without being interrupted. It's fun. BTW who are you using? I was using Scathach and Alice when I took on the final boss and was LV80ish.