Jak 3! At least that's the one I used to play the most.
I also played the first three Jak & Daxter games, but why exactly did you love the third one more than the others? I like Jak & Daxter 1 more than the other two, but I would personally still say the second one was better than the third one.
I got to play the first game only recently as part of the Jak & Daxter trilogy collection on the PS3. It's a lot like Crash in many ways! That's not a bad thing, I suppose, but personally I guess I enjoy the dark turn the series headed for with the second game.
I liked the story, characters and the city in the second game, but some of the objectives could prove to be really frustrating, at least for me. If the game had more checkpoints, or at least a selectable difficulty setting, I would've been more on board with it.
That's not to say that challenging games aren't fun! I just found myself frustrated more often than entertained.