Everything else being equal, a 2-blade prop is more efficient than a 3-blade. HOWEVER, seldom is everything else equal. On a fixed-pitch prop a 3-blade must be shorter than a 2-blade because of horsepower absorption. This makes the 3-blade quieter. 3-blades usually win in the take-off and climb catagory but suffer slightly in cruise. But this depends on the efficiency of the two props. In my situation (fixed pitch) my Sensenich wood prop worked great at altitude but my take-off suffered because at 640' elevation in Texas heat I could not turn up a good static rpm. I have searched for years for the right prop. My search ended with the Catto 3-blade. Craig worked with me to get the prop just right. Final result was a 17% shorter take-off. Noticable climb improvement and no degradation in cruise. And I won't even get into the sexy appearance and smoothness. This is my result...your mileage may vary.
Mel...DAR