This discussion has come around and gone several times. I have been continually altering the way I think, but I'm being swayd by the following:
Your choice of home defense load depends mostly on your opinion. The fact is that a round that patterns good in your gun will be just as effective on-target as any other load. This applies from 000 buckshot down to BB or even smaller. The problem with smaller shot is that you will lose penetration. While the shot wad will enter the body of an attacker, rapist, etc. as one large column, it will disperse quickly dumping its energy often before it can penetrate to vital organs or cause a massive enough loss of blood to stop the threat.
There is a school of thought that if you use a shell with a greater pellet count, you are more likely to get a hit on your target. I'm convinced that this is wrong at home defense ranges. At these ranges, the largest pattern you're likely to get is about two or three inches. 000 buck will be about that tight too. Further, a near miss with 000 might allow one pellet to hit. A single 000 pellet can stop someone whereas a dozen No.12 shot are not likely to have the same effect.
Another school of thought holds that you should use 00 buck in cold weather because it is more likely to penetrate clothing. True, to a degree. This is what I use... but for other reasons I'll get into in a minute. In reality, 00 buck and bb both perform about the same on clothing at HD ranges. They act essentially as a slug and have no problem penetrating. Smaller than BB, it starts getting iffy but you are still going to penetrate clothing well.
Here's my opinion of a slug. Slugs are good out to about 100 yards if you have a good load/gun combo, rifled barrel, scope etc. The range diminishes rapidly as you add factors such as adrenaline, low light, target identification, etc. The main problem is this: If you have a Bad Guy who is beyond buckshot range, is he still a threat? Should you still be shooting at him? I've heard of all kinds of fancy, half-thought-out schemes where people have one slug, one buck, one slug, one buck. Some even get fancier and have the first round a 'blank' or less-lethal round. Many will have the first two or three rounds buckshot and then a slug or two. At one time I had a sidesaddle with slugs because I bought into what people were saying. Me, I don't see the functional difference between a slug and Buckshot at Home Defense ranges. For deer hunting, they're fine, but for home defense they don't provide anything but overpenetration. My Buckshot loads will pattern very well and ensure a hit at any range I'd expect to be shooting at.
Some final thoughts on home defense shotguns. The chances are slim that you'll ever need to use the gun to defend yourself, so rest assured of that. If you need to use it, you are very unlikely to have to discharge the shotgun. The most important aspect of the shotgun is the intimidation factor. When a BG hears the slide cycle or the automatic's bolt close, he knows that his life might be coming to an end quite rapidly and violently if he does not halt his criminal intent. If, God forbid, you are forced to use deadly force, the shotgun is easy to point and will stop a life-threatening situation more effectively than any other gun. Besides that, they're dirt cheap and reliable as all getup. And sexy, let's not forget sexy.
