Sorry don't mean that 2 blades are more efficient but that fewer props the better in terms of overall efficiency. For that matter, higher pitch as well... but at the end of the day, it just depends on what you want it for.

small prop, high pitch = racer

large prop, low pitch = glider towing or 3D

3-5 blade prop = looks nice :-) and could be better for planes that have a big engine and want a little more prop clearance and don't want all that torquing that comes from big pitches

just my two cents! (which is probably worth less than that!)