I think you can look at the shapes of ship bows for your answer. A submarine is built for low resistance under the water and has a blunt entry. They can travel at speeds far greater than surface ships with less relative horsepower. This is because much of the drag on surface craft is due to energy spent creating waves at the water/air interface. Modern surface craft have a blunt entry shape below the surface that looks like a bullet (bulge keel). However, as you get to the surface, the bow will get finer until it is a relative knife edge at the surface as to minimize disturbance of the water/air interface (make waves). Since you generally want to keep your catamaran sailing on the surface, the fine entry is the way to go. The downside to the fine entry bow is that you lose displacement up forward and thus limit the amount of power you can carry in your rig with out turning your cat into a submarine (pitchpole).