"Be specific....I'm a gun novice."
Benn thinking about this, so here comes the lecture:
Shotguns are best for facing a mob or crowd. (That can be as few as one or two opponents, actually.)Pistols are for close-up, after they've gotten in too close for the shotgun, as a go-to-h3ll option. NOT recommended for primary defense, so if your funds are limited, go for the shotgun first.
If you're a guy, and average to large, anything in 12 gauge is good. Go for 00 (called double-ought) buckshot. I have been known to alternate 00 and slug rounds; I particularly like something called a "Brenke" slug, (spelling uncertain) as they can penetrate and take out people behind the one you shoot first. Most folks like shot loads only, though.
For smaller guys, and the ladies, a 20 gauge may be more appropriate. Children, too. Find a good (i.e., well-recommended) gunshop in your neighborhood, and talk to the folks there. Some have indoor ranges where you may be able to test-fire guns, and also take gun safety courses. I'd also join the NRA, and any other gun groups that strike your fancy. They offer training, and knowledgeable help in selecting weapons.
Size and recoil and comfort in holding and controlling the weapon are more important than brand names, but some of the weapons mentioned on this thread are there because they are known to be reliable and sturdy. You can't go wrong with any of them, and as far as I know, nearly all are available in a range of calibers (properly gauges, in shotguns). If you have kids, you might want to start them with a .410 gauge.
Hope that helps.
All this information and links to other information is great! Thank you to everyone that contributed. I'm savin' this thread!
Some may have heard of this round, I don't remember the maker, but my agency uses them.
The old standard was one inch of spread for every foot when it came to 12 gauges. But that's not applicable with this round. Instead of 9 shot inside it had 8. The first two are adhesed together inline and the other six are adhesed to them in a ball. The shot are all held together in one clump with the two inline shot leading the way. It all stays together until it hits something, at which point it seperates. It is good to 3" @ 50 yards if I remember correctly. So now you can have a shotgun round accurate enough to use in a crowd and the devestation on the target is comparable to arms length shot with a 12 gauge, but out to something like 15 yards. Then the effect is still extraordinary, but the loss of energy is such that it's not as spectacular.
I'll have to ask Tuesday what the make and name of the round is again.