Lots of recent threads on "which mode to use" or "who uses manual?". These are perfectly legitimate questions, I suppose, but all of the modes just apply varying levels of convenience to how the exposure triangle is manipulated to achieve the desired effect. As I described in the recent "Dew Tour" thread, I tend to leave mine in aperture priority...this used to be the only auto mode available on some film cameras, and in my opinion it's because this is the most useful mode for typical shooting situations. The reasons for this are two-fold:
1. Most consumer-grade lenses have a relatively narrow range of useful apertures; wide open isn't necessarily very sharp (nor very large... sometimes you need all the light you can get, so this is an area for compromise), and anything beyond F/16 or so can cause excessive diffraction. The best resolving power of the lens is restricted to relatively few f stops. On the other hand, shutter speed is shutter speed, regardless of quality or cost. That said, the range of available shutter speeds can easily exceed the useful aperture range of a kit lens. Just vary aperture within this useful range, and shutter speed will come along for the ride. Need max shutter speed to freeze motion? Just set the aperture to wide open; the shutter speed will automatically be adjusted to its fastest possible value.
2. Aside from panning technique and other motion-related effects, I consider aperture a more useful compositional parameter than shutter speed, although this really depends on the photographer and the type of photography.