I'm a big fan of this series. It definitely depends on what you enjoyed about each game. Personally I loved the setting in Persona 3 better. I felt like I was on equal terms with everyone else, and enjoy exploring the city life with my fellow classmates and the fact I was living in the dorms with other students. I also found that this game gave me the creeps sometimes with it's creepy atmosphere.

I also enjoyed the social links in Persona 3 a bit better than Persona 4. Of course the Female MC social links in Persona 3 Portable was the one I had fun with the most.

Persona 4 has many more options for gameplay. You can customizing your character's skills (personality traits in better detail), choose to get money, and social links. Also if you do prefer the country-side, small town, and family-oriented setting then this will be more enjoyable for you. The battle system is definitely a lot more refined, and makes grinding a lot more smoother. Also the difficulty in Persona 4 is much higher than Persona 3 Fes (excluding the extra story-mode).

Of course I definitely agree that Persona 4 Golden beats them all with the extra goodies and tweaks!

Happy Personaing~