The first shotgun I ever used, over 40 years ago, was a SxS, a 20 ga. Killed my first ducks with it, as well as a lot of rabbits.
I still have a soft spot for a SxS. A particular favourite is my Krieghoff, which not only has SxS 16 ga barrels but a 7x57R beneath, and yet weighs only 6 lb bare. That little gun handles and swings so nicely, even with its short barrels - only 22" or so. An ounce of shot, or maybe 1 1/8, seems to do anything I want to do with it, and I've taken various birds, rabbits, foxes, pigs, goats and other critters with it.
I also like the Brno ZP 49. These are a real sidelock, mine a dual trigger with ejectors and a straight-hand stock. Quite a light gun too, and again best suited to 1 - 1 1/8 oz loads.
I've shot a good number of others. A couple I remember fondly were my mate's Boss, which he inherited, a Dickson which another mate had, and (perhaps at the other end of the scale as far as fancy guns go) a Savage 20 ga which I borrowed one afternoon, with which I killed a running hare with each and every shot in the box of cartridges.
