Artificial heads are probably the best way to go, but if I was a beginner, then I'd start with the conventional method, where you rebuild the (cleaned) skull with clay, and poke a wire through the top of the head, and snip when dry. there are a number of relief cuts you can make. Along the side of the head starting at the ear hole, under the chin, along the top of the head, and some birds like Mergansers, Old Squaw, Wood Duck, Harlequin, Eider, and Scoter can be inverted through their neck. Pheasant and Grouse as well can be done without cutting a relief. The incision can be sewn, but superglue works just as well.
You can also cut around the bill, remove the head, clean it well, borax it and dry it, then rebuild it with Apoxie Sculpt, and I will guarantee that the skull will fit (if rebuilt anatomically), and that can't always be guaranteed with an artificial head. Like humans, no duck is exactly the same, but if you are mounting a mature bird, then most artificial heads will fit.
I went back, and started rebuilding my stuff, because I have the time to do so. There is some shrinkage when dried, but I like the challenge of rebuilding the bill with Apoxie Sculpt and a wet Camel hair paint-brush.
Here is a link to some of the best heads. Note the price of these heads. They're not cheap, but you could definately use these for competition.
Go to "browse all products" then to "bird mounting supplies" then to "artificial heads"
Please feel free to give me some more questions,