OK--this is what Parelli says about sidepulls: On the side-pull (the bridle you describe most likely has reins attaching at the side of the noseband rather than underneath). This encourages bracing in the horse's neck. A hackamore brings the feel from under the chin and encourages "uh huh" muscles instead of "uh uh", softening the under neck instead of building it.
On this list I've read that the sidepull is better than under the chin. Now I'm confused! V
