the biggest factor for my choice of HD gun is its ability to be readily available in seconds of hearing a bump in the night

having something that is ready to rock and roll in 2 seconds, no matter what caliber
trumps the better caliber weapon that is in your closet, or locked in a safe unloaded, and takes you longer to get ready to defend yourself
an intruder isn't going to wait till you load your gun
if the intruder is in your house, and your HD gun isn't readily available in a few seconds, you can kiss your a$$ and your family's a$$ bye-bye.

having multiple choices and levels of defense for HD is also an advantage.

Thanks for the info, but I was more referring to the fact that he owns one. . . or more 

I own one, or more, of each, actually.  And for my money, the M1 carbine is what I keep for my home defense.  It's lighter, more maneuverable, shorter, has a higher ammo capacity, detachable box mags, and still packs more than enough punch to dissuade miscreants. 

Now, for the zombie apocalypse, things change. 

 I think that even though a carbine is "best on paper", the deciding factor should be personal preference based on experience, and the specific circumstances each person and/or home may have.

For me, I'm about 80% pistol, 20% carbine.

The 80% pistol is because it is likely what I will have closest me to if something were to happen, and I am not in my bedroom. I don't just open carry it on my belt when I'm in my apartment, but that is more so because I tend to not where pants when I'm home... But generally I always keep it within arms reach. If I'm watching TV in the my living room, it's on my side table next to me. If I go to the bathroom to take a shit, it comes with me. When I call it a night, it lives on my nightstand. If I think I hear something that I'm not sure may or may not be something, it's what I carry to take a look to settle my nerves.

More often than not, it is knocking at my door. You see, I'm the Resident Manager for my apartment building, and it isn't uncommon for me to get random knocks on the doors from residents who need something. Much easier to take a look with a pistol, than a carbine. If it is someone I know and trust, I have a high shelf directly next to my front door I can tuck it, and then help them solve their problem.

However, the 20% carbine is for when I KNOW something is wrong. If I hear something that I do not doubt for one second came from inside my apartment, or if something is literally trying to kick my door in.

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US Carbine, Caliber .30, M1

+2
I own more than a few and this is a nice choice.

Let me take a moment to clarify my position (not that I have any particular significance).  From infinity down to, oh, 21 feet, I prefer a longarm.  If you've been to the range with me, you know that I am pretty  handy with a carbine.  Between 21 and 0 feet, I would prefer a handgun.  Given that there is infinity % more chance of me needing a longarm than a handgun, given my preferences, I'll stick to my carbine by the bed.  If they make it in my bedroom door without me being able to react, feel free to mock my choice!

Let me take a moment to clarify my position (not that I have any particular significance).  From infinity down to, oh, 21 feet, I prefer a longarm.  If you've been to the range with me, you know that I am pretty  handy with a carbine.  Between 21 and 0 feet, I would prefer a handgun.  Given that there is infinity % more chance of me needing a longarm than a handgun, given my preferences, I'll stick to my carbine by the bed.  If they make it in my bedroom door without me being able to react, feel free to mock my choice!

This is what I think it really boils down to, preferences.
Over penetration will be an issue with any effective round, even shotguns. We should all use what we're comfortable and familiar with when it comes to HD.
I have to admit that, in a stress situation, I would be more comfortable shooting an M1 carbine over an AR simply because I was raised shooting that type of longarm. The AR platform is relatively new to me and I'm still not completely comfortable with it.

It's the same thing with my 1911. It's immediately familiar when it comes to hand, I needn't think about its operation, it's instinctive. For you it may be something different, a Glock or a Sig.

Just my thoughts.

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I'd like to touch quickly on the subject of the manipulation of firearms and lights. I personally feel that every HD firearm should either equipped with, or "live next to" a light.

With handguns, you have a lot of options. You can go with a weapon mounted lighted or you can utilize one of the many "one hand flashlight" techniques that are out there. The drawback to the various flashlight techniques is now it takes away from your manipulation of your weapon.

With a long gun, you are pretty much stuck with a dedicated weapon mounted light (unless you wanna rock a headlamp). Don't get me wrong, I like and use weapon mounted lights... however it also involves a higher level of training and control to do so effectively and safely. Remember... whenever using any weapon mounted light, you are "bending" a few of the primary firearm safety rules. Namely, the ones concerning pointing your weapon in a safe direction... after all, you are essentially muzzle sweeping unknown targets before identifying them.

For someone living alone, this may not be a "huge" issue. For someone in a large household with family, roommates, pets, etc... This can easily lead to a dangerous situation if the person with the firearm does not have the training or control to react to an unknown variable. In a perfect world, there wouldn't be any negligent discharges... but people can be stupid, careless and scared.

Additionally, learning how to properly manipulate a long gun when maneuvering indoors (especially confined structures) generally has a higher learning curve than a pistol. That's not to say it can't be done... our boys overseas, and plenty of agencies do it all the time. It just takes a bit longer for most people to get efficient with it.

So there are plenty of other trade offs going in all directions when concerning what you decide to use. It is the users responsibility to understand what they are, make an educated decision one way or the other, and practice accordingly.

Moral of the story... Train with lights. Train manipulating your gun. Train doing both at once. Learn different and proper techniques. Learn them all. Find out what works best for your situation, and your personal level of skill. And then practice more.

Kriss Vector.  .45 ACP carbine. I own one and love it.

^^ Nice!

I have kids so everything is locked away.  Only have a 65 lumen light and a machete.

If I did have something it would probably be a 9mm pistol.   

I like pump shotguns but I'm kind of forgetful and might forget to cycle.....I play paintball and sometimes forget to cycle under stress.  Now if I were to have semi auto 930 Mossberg like Q.......

So if I were to use a long arm I'd probably use a carbine since I'm forgetful about cycling.   At least till I can get a 930 mossberg like Q........

Fwiw, one thing about a carbine like an ar is that there are tons of parts and accessories. 
Also, top tier ar's are really cheap at this time.

One of the other factors of a carbine over a shotgun is that I plan to get the family trained.  An ar will probably make it easier.....cheaper (22 lr conversion), less recoil & less manipulation

Good luck with whatever you choose!

Whatever you are more comfortable with is the right answer IMO.

Personally my AR 16" is the most ready. I have a pretty reinforced door so I should have sufficient warning to deploy.

Now that I think about it... Drills would be smart.

For me I carry a S&W 38 in a non-retention holster as soon as I get home. At night it's next to a tactical light at my bed side. Also keep an AR and mags in the bedroom ready to operate if something extreme goes down. I like the simplicity of a revolver especially if woken up at night and you are still groggy. I also drill regularly through the house both lights on and lights off.