I have to say that it depends on the installation. A pusher instalation has problems cooling. (Look at the big scoop on the 337). So it will have more cooling drag. The pusher has less drag on the airframe since the local airflow behind the prop is speeded up and then blows over the airframe on a tractor. I believe that a pusher will be more efficient IF the instalation is good. This is very hard to do. I believe there have been a couple of airplanes that have really tried to come up with a nice installation. The xmc was one the prescott pusher was another.

Oh, BTW I am not saying that it is practical in real life. If you look at most of the commercial airplanes (FAR 25) that have tried the pusher installation they have all had problems with certification and were commercially impractical. A few examples are the lear fan and the beech starship, come to mind. The piaggaio while it is a cool airplane probably fits in there also (am not sure if they have made money on them or not) Far 23 powered planes haven't faired well either really. The 337 is a cool airplane but it had many cooling problems, people taking off with the rear engine not running etc.

Steve