Will has an excellent article and video demo of the two stances including the hybrid stance.
I've always played with the hybrid stance but will try the pinpoint.
I've been trying to improve my serve by minimizing the effort and hitches that arise from too many areas where things could go wrong. So recently, I've switched to an abbreviated serve and have seen marked improvement in power and consistency.
I'm going to try the pinpoint stance to see if that helps improve my serve even more.