Oh hey, its Momiji!

P3: FES is my favorite. P4 kind of botched the balance and strategy of the games by relegating the Navigator role to being mostly useless, making physical centric players useless, the dungeon design leaves much to be desired (not that P3's is any better and MegaTen in general, but at least P3's main dungeon's sections are short and to the point) and the economy system is busted and makes grinding more necessary than it should be. P3 is definitely more user friendly. I feel the dungeon crawling aspect of P3 is superior to P4's but P4 is better with the social sim, side of the gameplay.

I also feel it has a better story since its easier to come back to it rather than P4's where once you learned who did it, the actual plot isn't as exciting. Though which has the better cast is debatable.

I don't like P3P, I honestly feel you lose a lot out of the game by dumbing down the interface of the world and Persona doesn't work as well as a visual novel style as you would think it would. I also hate how the girl's story was kind of lazy with the Social Links, largely just making her have no one but the party to talk to and only two actual new characters are introduced, making her version of P3's world feel smaller. They also added in P4's obnoxious "dizzy" status which really screws the player out of making the most of good fortune like landing a critical hit.