I have been playing PF since January and just finished RotRL (as the GM). My group consists of four members who enjoy a healthy balance of character development along with the mandatory combat, with an emphasis on enjoying exploring new settings. They don't like getting bogged down with excessive rules or spend too much time character hoarding/powering up. They enjoy building relationships with NPCs.
What's the next AP I should invest in? I don't have a ton of other books (Core (duh), Best I & II, Ult Equip, Inner Sea Guide), but would be willing to purchase more if crucial to the AP.
I have enjoyed running PF because I like the material provided in RotRL (personalities of NPCs and monsters, combat tactics, visuals). It gave me enough to run the game as I saw fit without number-crunching and starting from scratch. RotRL was a little too constricting at times (or maybe too linear), but there were enough bits to riff off of. I know APs are limiting in this regard, but I am just not able to commit the time to creating whole new storylines around gazetteer-like material.