If it is your only defense shotgun, and you don't have to worry about confusing operation/ unique manual of arms with another shotgun, the Benelli M4 / M1014 is king. Others may argue that pumps are more mechanically reliable, but that only solves the mechanical failure part of the equation, not incapacitated or stress-induced operator error. During law enforcement training (post qualification, other scenarios), I've seen numerous instances of the officer short cycling a pump. Quality auto loaders eliminate that problem, as well as the need for both hands being on the gun.
If you are 100% confident in your ability through repetition, combat proven 590A1 and older 870 will not let you down.
There are a lot of great shotguns that can serve the purpose, 590's, 870's, Beretta's, Benelli's. The big difference to me is in the controls. Things such as the placement and operation of safeties, slide or bolt release, etc. If you have the chance to handle a few different types you can get a feel for what works better for you. Personally, I'm partial to my Rem 31 riot gun. I've just carried and shot it to the point that I don't have to think about how to operate it, it just goes. It's what I pick up before I go out the door to check cameras or feeders.
Personally I believe any reliable pump gun that you can handle well is a good choice. If I want to be lazy and just fire from a secure position, I’ll take a Saiga with a drum.
Firstly, what works for me may not work for you, but my go to in my small home is my Mossberg Shockwave with Federal #4 buck mini shells. With the right amount of work becoming proficient with it and the correct configuration, it is a VERY capable tool. With the mini shells, specifically the afore mentioned load, I have 8 shots with less recoil and enough penetration to stop a threat but not over penetrate. In my house, that load will group a little over hand sized at my furthest distance. The original reason I went this route is I have two crappy shoulders and can't really handle much weight or impact into my shoulder but much prefer the threat stopping power of a 12 ga over a pistol. I can however run the Shockwave and Tac 14 fast, accurately, and comfortably. If over penetration is less of concern or longer ranges come into play they are still very manageable with Federal Flitecontrol 00 buck.
For really close quarters I use a Keltec KSG. Holds enough mini shells to quell a fair sized invasion and enough 2-3/4" shells to handle any "normal" home emergency situation. But practice with it a good bit to get used to its operation.
I also have a 1301, 590 and Saiga w/ drum that I am comfortable with.
I like an 870 because that's also what I have used for most of my life to duck hunt. I am 100% comfortable with one and have shot thousands of shells with them.
For me the Mossberg 590 with 18.5 inch barrel, magpul stock with 1 spacer, and bead sight works - it patterns S&B #4 buck pretty good within 20 yards so I keep that handy. Very fun!
Whatever you go with, make sure the ammo you choose patterns well within the distances within your home.
I like a youth model 870 in 20 gauge, light and handy enough for my wife to handle and packs enough of a punch with the right load. And cheap, you probably got one already if you had kids.
They're whispers if its real or not. Legend has it goes by the name "Boom Stick" 10ga 3.5 in NEF partner SB2 turkey 18 in barrels tight choke. Weighing in at 7.58 lbs. It's basically like firing a shoulder cannon. Close quarter / door breacher.