I went through this with my daughter. Ended up with a 20ga Beretta 3901 and have been very happy. VERY reliable gun with soft recoil. The gun also has synthetic stocks, 3" chamber, choke tubes, etc. ALSO came as a youth model so it fit her (and my wife) right out of the box.
One thing to keep in mind with recoil and non-toxic loads......... Steel is light and kicks way less than the tungsten shot which is heavy. The expensive tungsten based shot is KILLER stuff, but it kicks more because it is a heavier. My suggestion would be steel for your regular waterfowl hunting, but switch to tungsten for the swans because of the size difference. You will be a little handicapped with the 20, but not much.
