I´m just being curious here but I also think it would be important to know (for me and everybody else) which is the most efficient collider, in order to use that one (and not other) in case you could chooose. I would say the most efficient is the sphere, because of the obvious radius test, but that involves root squares, so maybe the box would be faster… Well, I don´t really know for sure so: please, enlighten me with your deep knowledge of unity colliders.
I would bet on the sphere collider too - root squares are quickly calculated even in many mobile devices, and sometimes they can even be completely avoided (comparing squared magnitudes directly). Boxes are more complex, because rotation must be taken into account. I suppose that capsule colliders are in between, and the worst case obviously is by far the mesh colliders.