In my battery I have a Remington 870 and a bandoleer of slugs and buck ready to go for when the SHTF. You don’t lose much with a 20 gauge at close range either, and you gain some agility with a smaller gun, and more family members are likely to respond better to the 20.
The second point I’d like to make is on handguns for home defense: Shoot the biggest cartridge you can handle. That means a .40 S&W, a .45 ACP or a .357 magnum. Ask a doctor in an urban area where shootings are common and you will find these result in the most one-shot kills.
A 9mm? Well, if that’s what you have, use it, but they just can’t compare to the bigger rounds. I’m not a caliber snob myself, but face it: Bigger is better if you can handle the gun. And again, I’m not talking about concealed carry which can dictate a smaller round because you just can’t carry a larger gun at times, but I’m talking about guarding the homestead and your bedside piece.
But what is the best home defense gun? A rifle carbine.