The comments on fly and try are right on. I generally start out with an APC, but I may end up with something different. The last round of testing I did, I ended up with a best prop and three others, quite dissimilar, which were almost as good. None were APC. I've done the bit of taking engine, fuel, fuel tank, best prop, etc. and putting them in another similar airplane, and they don't work worth a darn. Go figure!