Which?
Looking ahead to invitation for dove, quail & pheasant hunts, this old goat so-far-rifle-only-deer-hunter wants to get a "bird gun". FWIW, and for no particular reason, I'm enamored with the over & under. Just need some help deciding if I'd be better off with a 12 or 20 gauge.

If I could have only one I'd choose a 12 unless you're recoil resistant.

20 is plenty good for dove and quail, lots of folks shoot pheasants with them as well, I sure like the 20 and 28 gauge better than a 12, hardly ever pull a 12 out anymore.

for dove,quail and pheasant hunting,get the 20 gauge....both Browning and Beretta make great 20 gauge over/unders...

This works for me.

20 no question

12. The more pellets in the air , the more likely you are to hit something.
Mo

410.... give the birds a chance.

That Ruger Red Label is on my wish list and has been on my wish list a long time. 12 or 20 would work for all you're looking at. I shoot only a 12, I need as much lead in the air as possible

Do you shoot a .243? If so get the 20ga.

I have access to both but tend to pull out the 20 more often.

12 is better all around. With a 20 you will be limited to dove and quail for the most part. If you get the opportunity to hunt ducks, geese, turkey, etc, you'll be a little under-powered. 12 will work fine for all of the above. Get good with it and buy a 20 down the road if you want more of a challenge.
And someone is going to get on here talking about how their uncle took an elephant with their single shot 20 gauge, but I promise a 12 is a better all around gun if you are only going to own one shotgun.

12, either pump or semi. The over/under leaves you 1 shot short. I need every advantage I can get.

How proficient are you? Going down to 20 or 28 gauges from 12 is going to significantly reduce your margin for error.

Recoil is also a factor to consider. If you're getting a little older and more fragile, a 20 gauge might be a better option for an O/U. Felt recoil on an O/U will be much greater than that of an auto due to the lack of an action. If you're still in decent shape, go with the 12.
That being said, if recoil truly is something you are considering as a factor, I would look into an auto. Gas operated actions (and even some inertia operated) have come a long way and it is possible to find a 12 gauge semi-auto that kicks no more than a .22.