Remington 1100
I like the Remington 1100 in 12ga. A couple of years ago I was also debating on which semi-auto shotgun to get (Remington, Beretta, Benelli, etc.). I ultimately went with the Remington 1100 and I'm very happy with it.
It's very reliable (gas operated), soft shooting, durable, and fairly affordable (although the retail price has gone up a lot since I bought one a couple of years ago). I use it mostly for clay use and it works well, even with light target loads. It patterns well and also fits me pretty well. For my needs, it is a good all-purpose semi-auto. Also, although I don't take such great care of it (I don't really clean it too often) it still keeps on cycling reliably.
My 1100 came with a 28" barrel. However, I also picked up an extra 22" barrel that has a fiber optic front bead and a metal mid bead for fun. It's actually the same barrel that is sold on the Remington Competition Master 1100
http://www.remington.com/firearms/shotguns/1100_competition_master.htm).
The only drawback with the 1100 is that if you want to shoot 3" Magnum shells out of it, you're probably better of getting an 11-87 or some other gun. I believe that most of the 12 ga 1100's are configured for 2-3/4" shells, although I seem to recall there is one version of the 1100 that accepts the 3" long shells. I prefer the 1100, because it more reliably cycles the lighter target loads that I use than a 3" gun.
Definitely check the 1100 out. You can probably find a good deal on a used one in your area.