Deborah:
As many have already stated, barrel length on a field gun is a matter of personal preference.
I hunt the same game you listed, plus waterfowl, turkey, pheasant, and chukar. I do most of my hunting in the High Desert country of San Bernardino, Kern, and Inyo Counties, as well as the mountains of the Central Coast and Mendocino County.
I am positively addicted to sporting clays, too. I also shoot a little skeet and trap, to keep life from getting too "samey."
But I do almost all of my shotgun shooting with one gun. That gun is Remington 870 with 28" barrels -plural in my case because I have both the 'standard' and Remington's 'light contour' barrels for it in the same length. This allows me to tune the swing of the gun a bit for the game I'm playing or shooting.
It ain't trendy, and it ain't cool. No one goes "Wow! What an awesome gun!" when I pull it out of the case.
The point isn't to sell you on an 870 but to illustrate how much personal peference can influence one's gun use decisions -including action type and barrel length.
I shoot an 870 the most because it is what I like to shoot and of all of the guns I have, it is the one that I get the most consistant results with, both on clay and in the field. The 870 with a 28" barrel simply feels like an extension of my body. I just shoot the thing and don't have to put a whole lot of thought into it.
Our female staffer on Uplandhunter.net feels the same way about her 28" 12 gauge 11-87. Like me, she has other guns to shoot (including a 12 gauge 870) but winds up doing the bulk of it with that one gun. A 12 gauge 11-87 with a 28" barrel was the first gun she ever shot and the gun that she started out with. Ask her why she still uses it, and the answer she typically gives is "Because it's comfortable and familiar, and I hit well with it."
We both shoot and hunt with the same group of folks. One fellow has a gun for every possible niche of shotgunning. He can switch from one gun to another and do well with all of them. Another female shooter that is a part of this circle of association shoots a youth model Beretta 391 20 gauge with a 26" barrel on everything. Another fellow shoots nothing but Browning Superposed guns -one for skeet, one for clays, one for quail, one for ducks, and so on. We all shoot the same games and hunt the same game, but none of us use the same kind of gun in the same situation. I am usually the only one shooting a pump out of this group of primarily Beretta and Browning shooters.
That's really my point. There's what works for me and what I like and what works for you and what you like, and they may seem as different as night and day yet deliver a similar result in our respective hands.
The beauty of a pump or autoloading repeater is that if you found that you bought the wrong barrel length, you can fairly cheaply correct that by buying a longer or shorter accessory barrel. My vote on this type of gun would be for the 28" but yours might be for something shorter.
-JP
www.uplandhunter.net