I think B looks the nicest of the three by far. Good use of a monochromatic color scheme, nice balance between background and foreground elements, perfectly readable at a distance.

The design direction of A is a bit busy and stands out a little too much IMO, it looks kind of out of place next to stock iOS apps. C looks a bit too amateur, and has several tangents in it that really bother me - I do like the overall idea of it, but it could really use a rework.