I prefer Ghost Hunter and Firefighter almost the same, with slight advantage to Ghost Hunter. It's colorful, dynamic and a lot of fun. I love collecting spirits:=)
I tried PI several times, but never get to like it, it was too boring to just click on icons all around, like in WA adventures, you get those boring adventures to go around ask/take/deliver things, and then you get real adventure to raid a tomb. I always prefer dynamic and more involving tasks.