The pusher/tractor debate is an old one, but it continues to inflame passions. One reason for its persistence, I suppose, is that propeller efficiency, considered scientifically, is a very complex topic involving many different variables and subtleties, and it is hard for a nonspecialist to understand. From the specialist's point of view, most of the interesting aspects have to do with blade geometry -- number and shape of blades, speed, spanwise distribution of area, twist and downwash, airfoil shapes, compressibility effects and so on. These are characteristics of the propeller itself, removed from the influences of the airframe to which it will be attached. Compared with a propeller spinning in aristocratic isolation inside a wind tunnel or a computer's central processor, the practical device attached to an engine and mounted on an airplane is a slum dweller.