which is the best 2D game enginefor iOS?

I really need a game engine that allows me to modify the game code because I need to control the multi-touch events. I have a framework that detects the gesture that the player makes and I need to test this gesture recognizer in a game, so I have to have the freedom to change the game code. I don't want anything like GameSalad where you can't control anything.

Thanks in advance.