Guns, chokes, loads, and guage questions are quite subjective, and everyone has their own opinion. He's mine. Hopefully it helps.

If your going to get a new gun, get one that fits you properly. One will shoot a properly fit gun better than they ever thought possible. If you aren't sure about gun fit enlist the help of the professionals at a gun shop or grab a book on the subject. If the gun fits you will shoot it well, and guage selection becomes a little less important.A proper fitting gun, because you will shoot it better will allow you to be more effective, and feel more confidentwith a lighter guage.

As for choke selection, I follow the standard that the closer the standard shooting range the more open the choke. I hunt almost exclusively grouse and woodcock. I either use a 20g s/s choked sk/ic, or a 28g o/u choked sk/sk. Again, if the gun fits, the pattern will go where you point the gun, so choke selection becomes a little less important.

Remember too, that a smaller guage gun doesn't mean less pellets in the pattern. An ounce of #6 is the same number of pellets whether packed into a 12g hull or a 20g hull. The only thing that changes is the length of the shot string.