I think it is impossible to say just one breed is the best bird dog. I think there is suitable breeds for different birds and type of hunting. Here in Turkey we prefer English setters for woodcock hunt and pointers for partridge and quail hunt. I have a breton and according to me this breed is very efficient in pheasant hunt. It is really very difficult to say one breed is very efficient for hunting every kind of bird. But generally GPS and Drahthaars versatile dogs. So they can be adapted for every kind of upland game hunting easily. But they can never be an expert. It is not possible to do every thing perfect; you can do some of everything. Versatile dogs to some in every hunt but i have never seen an expert.
It is the same for dogs too. I prefer experts and hunt with different type of dogs for different type of games (also weather and plant cover)