I've owned many shotguns; my favorite was a Winchester o/u pigeon grade with screw in chokes that my wife bought me to gun in bird dog & retriever field trials. I ended up using it for that and for pheasant and ducks. Two things are key: fit (get someone who knows how to fit you) and an accurate, reliable, adjustable choke. with 12 vs 20, remember you can always use light loads in a 12. I had a couple of 20 ga doubles (including a citori) that I liked for rabbits and quail, but I like the o/u 12 for pheasant, etc. I actually preferred a heavier gun for pheasant and ducks. My lightest 20 double kicked like a mule.