A good duck gun is one the fits and feels good in you hands and patterns the loads you shoot well. Outside of that what ever meets those criteria anything goes.
My first shotgun was a Ithica 37D. I switched to an O/U some thirty years back and although I own a few pumps and have had autos it' s an O/U that gets the call for all my hunting and clay shooting.
I' m not going to tout on gun over another ,but will say learn the art of waterfowling and time in shooting clays you' ll never need to shoot a 3 or 3 1/2 mag.