For most users, it doesn't really matter what shotgun you get. I'm assuming that you're an average user who wants it for home defense. An old J C Higgins pump that left a Sears show room when LBJ was in the White House and a few minutes work with a hacksaw and files is going to work about as well as today's latest and most expensive gun.
That said, I would look for a POLICE MODEL 870, not one of the HD or Express guns, or even the new tactical ones. I'd look for an old Police Model stamped gun with rifle sights. Just get the forend cut/sawn so that it doesn't block the loading port down below. Many used guns will have had this done already.
Some users, such as the Marines, benefit from the added marginal utility of specialized guns such as the Benelli autoloaders. Tricking out a Saiga is another option. For most people, it doesn't matter so long as the gun works and hasn't had holes rusted right through the receiver.
If you need to engage targets at 100 yards or more, you need a battle type rifle or carbine. Unless it is bears in the yard, then you need a dedicated dangerous game rifle.
I think Wilson products - 1911s, magazines, and what not are overpriced for what they actually deliver.
My current household shotguns are two Mossberg 500s, a Winchester Model 12 made in 1919, a JC Higgins pump so old that there's no number on the receiver, a Remington Model 11 that's so old it has the trigger style safety, a Stoeger coach gun, a cut down NEF boom stick, and a youth 870 in 16 gauge plus a 20 gauge Winchester 120 with a long cylinder bore rifle sighted deer barrel on it.
I do wear body armor. However I have long arms. Thus the stock length on most guns is fine for me. On the Model 12 and Stoeger, I did fit slip on recoil pads since these guns tend to thump the user otherwise. Even my tac armor isn't the type that makes it that hard to shoulder a weapon.