Critical characteristics are for the knife to have a good grip that won't slip when wet and has some sort of protection to keep your hand from sliding down onto the edge. The point should be fine enough for easy penetration, but not so fine as to be weak to break or bend easily. The blade doesn't have to be heavy or thick, but it shouldn't be so thin as to bend or break easily. It can be straight edged, bellied or recurved depending upon how it will be used. Bigger is better, but only so far as you can carry and use it.