Not a bad idea at all. Your taxidermist will actually appreciate it if you brought in several ducks to choose from. You said you were not sure which birds were in better shape, and that is the first time I ever heard someone admit that he may not know this. Some guys look at this newly killed bird and say he's just beautiful, and quite often it's a taxidermists nightmare. Problems can range from a dog with a hard mouth to a nasty shot at close range to a early season poorly plummed bird, or an immature bird all together. Needless to say they all suck to work on. Your taxidermist will like the birds your bringing him, because they are some of the toughest skinned birds to work on. I have a hen and drake of each in my collection, and both species are gorgeous birds. What time of the year were they harvested? I can give you an idea if their plummage will be worthy of being mounted. If your taxidermist says he'll get rid of the other birds for you, there's a good chance they're all in good shape. Congratulations on your first step into a sick addiction. I have over forty birds in my collection!
Wings cupped, Pete