I like, and hunt a great deal with, single shot shotguns...12 and 20 guage. Part of it is that I don't want to wipe out the pheasant population around here, so I figure I get one shot at the birds the dog and I find.

Call it "flight training."
Both guns are old...and the 20 is a rescue from a farm...dented barrel end, lost fore-stock, and rusted action. Cut off the end, fabricated a foregrip, and cleaned up and loosened the action. The 20 is probably an open cylinder now, which is fine. I use it for walks along the crik, puddle jumping ducks, and in an area that adjoins the crik with 10 yards of cover, so if a pheasant flushes it will be within range for a while, anyway.
(Gotta tell this: the dog and I went out for a crik walk hunt. Snuck away from the crik so any birds there couldn't see over the bank...came up upon some, they flushed and I got a Mallard drake. (Steel shot #4).
Continued and let the dog mess around in the brush at about the point we turn back. Heard yelping, and darned if a bunny didn't run into an area in which I shot ! Not bad, eh?
Then, walking up to the house, the dog got birdy...and I scoffed...but followed, and there, in a spot in which no pheasants had ever appeared, flushed a rooster! I hit it. Dog retrieved it.
Three species, one beat-up hunter and shotgun. Never before, never again. But it was neat.)
Dunno if it is worth it to you, but interchangeable chokes on a single are very unusual. Most are full. You MIGHT get an older single 20 guage used, and have a gun smith thread for some mfr's chokes, but it would depend on the gun and the gunsmith. maybe some of the high-priced makers would make a single which has multiple choke options, but be prohibitively expensive, from my point of view.
Good luck. Report back, will you?
Kis
enjoy every sandwich