That would depend on how exactly your game is going to work. Unless objects need to bounce, or you want some fancy soft-body physics you probably won’t need a physics engine. Finding intersections between sprites (objects on screen) can be easily done using some kind of RectIntersect algorithm. (CCRectIntersect if you’re using Cocos2d)
If you find that you do need a physics engine, Box2D is probably the better option. Not necessarily because it’s better, or more fully featured, just because it has so much more information available about it. It’s been around a long time and there’s hundreds of tutorials and forum posts that can help you track down errors very quickly.
Just a word of warning though; removing Box2d objects can be a pain in the ass, you’re going to want to look up a few tutorials on how that can be done without causing your game to crash randomly.