BTW, lots of good gun info in this thread. I'm not looking into a carry permit or getting a handgun now, but I'm seriously considering a rifle or shotgun for home defense. Good to learn a little about firearms before then.
Shotgun, definitely. Rifles are horribly impractical for home defense. Too much penetration. That bullet goes into your neighbor's house and injures someone or even kills them? YOU are 100% responsible. Doesn't matter if you were aiming at an armed home intruder. Let's say you nailed him. That rifle round could still have enough energy behind it to keep traveling beyond his body, out your home, into the home of a neighbor and enter the body of an innocent resident.
Rifles are made for penetration at long distances. Thankfully shotguns can be loaded to greatly reduce the likelihood of over-penetration. Obviously, don't use slugs. At the extreme other end, don't use Bird-shot. No risk at all of over penetration, but no real stopping power either (unless your armed home intruder is a pigeon).
Semi-auto shotguns are expensive, plus most of them look way too tactical. Use one, and a jury of our peers here in NYC might decide to convict you just on looks alone.... of your shotgun. A good pump-action is overall the best choice. Avoid the Maverick 88. Popular choice. Especially in terms of what you get for a very low price-tag brand new. Problem is, those advocating it have never dropped one onto the ground. Ridiculously easy to render it inoperable. Remington 870 is overall a solid choice. Used by a huge number of police departments. Even to this day. A no-frills police turn-in is a good idea on the used market. One thing though, you have to load the shells PERFECTLY into the bottom, or it can seize up. Doesn't happen often. But often enough where it can be an issue. Mossberg 590 is another excellent choice. No need for one of the fancier versions. Though I do prefer the location of the safety on the 870, instead.
Very controversial aspect is the level of training needed to use a pump shotgun properly. In the heat of the moment when you need it, it's actually possible to forget to pump after each shot. You get off one shot, the threat is still coming at you. You didn't dedicate enough time and practice to your pump shotgun. So, you just stand there pulling the trigger again; wondering why your shotgun isn't working. That's a very real thing, it does happen!
One way to negate it, aside from tons of practice and training is to get a double-barrel shotgun. There are going to be folks who will despise me for making that recommendation. I see it this way.... Having two shots for sure, is much better than having one; and forgetting to pump. Much better. Easier to learn and practice with. Yes, for those in law-enforcement who literally go in harm's way; it's a stupid option that thankfully was phased out in America many decades ago. But for a home owner, it's still viable. Plus, you can say you're getting one for "Sporting Purposes" in order to prevent the holophobes from getting horribly upset and violently urinating on themselves in their collective outrage!
An Over & Under double-barrel shotgun for example is the most common type used for shooting clay pigeons. Avoid the ones made to look "Tactical." Brands to check out would be CZ, Mossberg, Winchester, Savage, and Browning. Though one aggravating issue is that these types usually come in the longer barrel lengths of 26"- 28" that are far from ideal for home defense. Ironically, Side-by-Side doubles can more easily be found in shorter barrel lengths.
If you prefer a Side-by-Side double barrel, look at the more traditional offerings from Stoeger. While a double trigger is okay, do NOT buy one with exposed hammers. Those need to be manually cocked before firing each barrel. Something very easy to forget to do during the heat of the moment.
Best choice in gauges: 12 or 20. Best not to go smaller than 20.
12 is ideal for men. 20 is more for women, or elderly men.
Hope this helps a bit. But please do more research on your own before coming to a conclusion.
EDIT:
Typo.