It is possible to make an argument for almost any type of firearm for home defense.

While no one argues that a 12 gauge is effective, you have three common counter-arguments: (1) possible overpenetration; (2) excessive recoil for women or younger members of the household; and (3) it is easier to take it away from the homeowner.

Yet, ammo fixes (1), changing to 20 gauge fixes (2), and making sure not to let the barrel go through the door or around the corner too much ahead of you fixes (3).

As to carbines, the 5.56 with proper loads will actually penetrate through less drywall than the 9mm as shown in tests conducted at Gunsite and elsewhere years ago. And, its recoil is easier managed than either a 12 or 20 gauge.

Then, there is the cell phone, flashlight, and spare ammo issue. As Clint Smith says, you will likely fight with the ammo in your gun or on your gun. Thus, get a butt cuff or other ammo carrier for your shotgun. A sling is also a necessity. Mount a flashlight. This is easier to do these days with shotguns designed for such.

Repeaters are better, but you can make do with either a short barrel over under or even a short barrel single shot. By short barrel, I am referring to 18.5 inch, not one requiring a tax stamp, although the new Shockwave is an interesting idea, especially with the clip-on adapter, and mini-shells, to increase capacity.

As to pistols, it seems like a good idea to use a high capacity 9mm with an extended magazine and light mounted on the pistol.

Massad Ayoob came up with a Beretta 92FS years ago, and it had a light, and extended magazine, and an extended Jarvis barrel, if I recall.

The Glock 17 or 34 seems like a good idea these days, with a light and a 33 round magazine.

If you are going to venture out to conduct a search of your own house, a shoulder bag with a cell phone is a good idea.

All of that said, home defense is best conducted with a proper state of mind. The tools your grandfather used for the same purpose will still serve well if you have the right state of mind.

So, in those jurisdictions where you can only have a single barrel or double barrel shotgun, practice quick loading, and mount a light if you can, and don't forget to yell, "welcome to Scotland" when you blast the intruder!