Hi,
I think that most of the time, a blunt nose is best -- because the air "decides" which way it will flow, and this determines the stagnant point.
But, if you use a pointy nose that is as low as possible, then this forces more of the air to go up an over the car -- which can be helpful especially if you do not have a smooth underside.
For example, my rear wheel skirts get pushed outward; I think by the air coming out from under the car, as well as by air on the sides "catching" the bottom edge. OTOH, Chang's CRX HF has a long and low and quite pointy nose, and I think this helps minimize the need for a belly pan.
