On twin-humbucker guitars I use all three positions, depends on what sort of mood I'm trying to convey. If I want to cut and "stick it to the listener" I'd be on the bridge, but for some reason I think of the neck as more "emotional". On the middle position, I can use the twin volume knobs to blend them to get sweeter or more angry.
However, I'm really a strat player, and like all my heroes on strats I'm a compulsive knob and switch twiddler - I use all the positions for a different tone of voice.
One thing I just thought though - do you play/rehearse in a band? Remembering back (years now) I couldn't make much sense out of a neck humbucker until I was playing through an amp loud enough to get over a drummer (and part of it was fighting with the drums as well) suddenly it seemed to make sense - before that I was always using the bridge...
