First, I don't understand the comments about scaring away intruders with the sound of 'racking' the shotgun. Why would you give away any tactical advantage you have by announcing your presence, possibly your location and the fact that you are armed with a particular weapon? Especially if you don't know where and how many attackers you're facing? Second, why isn't the gun loaded and ready in the first place? Is one waiting for the last minute to chamber a round? What if you get surprised by a hidden attacker? Or one that moves quickly? Or what if the attacker is basically chasing you and you only have time to reach the weapon and shoot - an empty weapon will be a liability at that point.
If you have a weapon that you intend to use for defense, it should be loaded and ready (but in a safe condition) at all times.
A shotgun is probably not my first choice for HD. I've tried shooting handguns, shotguns and rifles this year. The benefit of a shotgun is that, depending on the setup, you may not have aim precisely. On the other hand, that could be a cause for concern. The problem is that they tend to be very unwieldy -- they are long and heavy and not very maneuverable. That could be a problem in itself.
Not meant to be comprehensive and there are exceptions. Just some thoughts that come to mind:
Handgun (semi-auto, not revolver):
pros: maneuverable. light, easy to carry. easy to use ambidextrously. multiple rounds before needing to reload. easy and fast to reload. easy to use with a hand held light. good for corners (if you absolutely must walk -- ie - to get to your kid's room)
cons: harder to aim and use quickly for distances farther than 7 meters (which may be sufficient for households). Keep in mind that 7 meters is only 2 seconds away. may require multiple shots to stop a threat. aiming / shooting quickly is a perishable skill.
Shotgun:
pros: potential for wide shot pattern. effective in stopping a threat. rifles are quick to aim (less skill required). good for when you are covered behind a choke point.
cons: heavy and hard to maneuver. limited number of rounds before needing to reload. slow reload. not easy to use with hand held light. not a good choice for corners. recoil may be too much depending on the shooter. depending on action, can be subject to misloading issues.
Rifle (AR15 type):
pros: very precise. quick to aim (less proficiency than handgun required). effective rounds. multiple rounds before reload required. easy and quick to reload. round generally tumbles and becomes ineffective after passing through barriers. minimal recoil - easy to manage for quick follow-up shots if required. proven reliability.
cons: harder to maneuver relative to handgun. not a good choice for corners.
For me, in my house, in my location, I would choose an AR first with handgun backup.
Caligirl, you want to use something like a jacketed hollow point (JHP) for handguns. Gold Dot is a popular brand.
Whatever one chooses, it only counts if you can hit the attacker. I recommend you try shooting each choice at a range that allows you to shoot quickly, shoot multiple targets, shoot moving targets, shoot while moving etc (all the things you might be doing in a real situation) at different distances you deem appropriate for scenarios you think likely.
Different people in different environments in different situations call for different tools and tactics. Try before you buy.