They are about equal in my mind, honestly. I pretty much like the aspects of both of the games that have already been mentioned above. I can say I vastly preferred the TV World over Tartarus for the most part.

I liked the cast of both games about equally for different reasons. P4's cast annoyed me less throughout the game, but I did kind of like that the team in P3 didn't necessarily all become the closest of friends like in P4. I do like that you can have social links with all of your team in 4; and like White Wizard said, I'm happy that you can do a friendship route for the girls. That being said, I kind of wish there was more to the friendship route. You get a little more interaction when you become romantically involved, and that bothers me a little.