Guns: 12 vs. 20

The most popular shotgun gauge, by a huge margin, is the 12 gauge, with the 20 gauge capturing a fraction of the market, and the rest of the gauges (.410, 16, 28, etc.) struggling to even keep up. This is a bit odd to me - having owned a shotgun in 20 gauge, and the exact same model in 12 gauge, I can safely say that the 20 gauge pointed better, carried easier, had less recoil, and was just as useful as the 12 gauge, at least for skeet and trap. 20 gauge shells are also available almost everywhere 12 gauge shells are sold.

The one thing 20 gauge may or may not be up to is home defense, which is certainly a valid reason to own a shotgun (and perhaps is the primary motivation for a lot of people). Buckshot and slugs, the only real options for defensive shotgun use, are in limited supply for the 20 gauge. I used to have a package of Remington Express #4 buck that I kept in my old 20, but it certainly wasn't something you'd find on the shelves of most Wally Worlds.

In any case, the 20 gauge is pleasant to learn on and pleasant to shoot, which will probably ensure its survival.