The question of what gun to use in bird hunting is interesting - but personally, I use the same gun in the field that I use for Skeet and Sporting Clays.
I prefer all of these pastimes - with an O/U that is in the 8 1/2 lb range. A light gun in my hands - is way too whippy - and I have a tendancy to cut off my swing and follow-thru / so I weight my 20ga, 28ga and .410 to about 8 1/2 lbs vs the 7 1/2 lbs they come out of the factory ( all Browning O/U's, with 30" barrels ) in all 3 gagues....works the best for me. Note: I don't hunt with a .410 / but I do hunt with a 12ga, 20ga or the 28ga ... and on birds like Quail, especially over good dogs, a 28ga is a great option.
By the same token - when I travel by air / and only want to take one gun - I will always take a 12ga / and load it down to 7/8 oz or 1 oz depending on what I want to do with it. My favorite Travel Gun - is a Benelli Super Sport semi-auto 12ga - with a 30" barrel ....and at only 7.25 lbs its a great gun to carry in the woods as well ( and shoot a little Skeet or Trap - or waterfowl with it too ) ... So maybe I don't know what the best answer is - other than - do whatever makes you happy .