After some of the responses to my Hell Diary I figured I better go with something a bit less controversial...
The most basic of all human rights, or really animal rights, is the right to defend yourself if attacked or in imminent danger of being attacked. Call it a biological right. In humans, and all territorial animals, this right (and the impulse to exercise it) is strongest close to the center of an individual's territory. For people, that's their home.
I realize that there are extreme anti-gunners who will object to the mere notion that anyone should act to protect themselves or their family when they could just sing Kumbaya to any intruder, but fortunately this is a mental illness that afflicts very few. Across the jump I will discuss guns, evil firearms; in particular, I will be addressing guns intended to shoot people. Please flee now if the very notion offends you.
When most people think of a firearm for self/home defense they think of a handgun, pistol or revolver, practically by default. In well-trained hands a handgun can be a safe and effective means of defending yourself or your family, but they require by far the most training to become proficient with and require frequent practice to stay proficient with, and are the most hazardous type of firearm to have around small children. Additionally, those in the upper power range can pose a serious overpenetration hazard that can endanger other occupants of your house or even neighboring homes.
I recommend handguns only to those willing to commit themselves to the necessary training and continuing practice required to acheive and maintain a high level of proficiency with one; in other words, those who don't need my recomendation to start with. They are a poor choice for anyone who intends home defense as the only role a gun will play.
Before I move on allow me a cautionary note: there are a million cheap .25 Auto and .32 Auto pistols, by a variety of manufacturers, floating around this Country. Without exception, they are worse than useless for any purpose other than paperweights, and should certainly never be loaded.
Rifles are not really ideal for self defense in the home, but are somewhat easier to learn to use safely and effectively than handguns and require less frequent practice to maintain a useful proficiency with. Generally much more powerful than handguns, they pose an even greater overpenetration hazard. The sole exception would be a semi-automatic .22 rimfire, which is easy to learn with, inexpensive to practice with and extremely unpleasant to face in a dark house you have no business in.
Probably the least suitable rifle for self/home defense under almost all circumstances, with the exception of an elephant gun, is anything anyone would call (rightly or wrongly) an "assault rifle". Most people find them awkward to handle without LOTS of practice, they invariably overpenetrate at close, inside-the-house range, most are too complicated for use under high stress and, frankly, there are better options, which I'm getting to.
NOTE: If Blackwater ever deploys extensively within the United States we'll revisit rifles.
For my money, any person who wishes to be able to defend their home and those in it from unwelcome intruders really has only one optimum choice, a pump action shotgun, in either 12 or 20 gauge (there's little practical difference in this application). It is the ideal home defense weapon for several reasons. It is simple for an adult to operate, but very difficult for a small child. It is devastatingly effective at close range but, properly loaded, poses little hazard to anyone but the target. It is easy to learn to use effectively, and has one feature practically no other available option has, a definite last-chance deterrent effect. There is no more distinctive sound in human society than that made by the cycling of a pump action shotgun in a dark house; every criminal alive will instantly recognize the sound and it's implications, and most will immediately endeavor to elsewhere forthwith, without the gun ever being fired or anybody getting hurt, a near-ideal outcome.
Nothing fancy is required for a home-defense shotgun, there's no need for doodads hanging off of it or long, extended magazine tubes. A basic model from any major American manufacturer (Winchester, Remington and Mossberg are the most common) will do nicely, and Remington and Mossberg produce "Youth" models proportioned for adolescent boys that also fit women and slightly-built men, and they are readily-available anywhere that sells guns. Pay no attention to anyone who tries to sell you a folding stock or pistol-grip or anything but a basic pump-action shotgun.
The biggest load of nonsense peddled about home defense shotguns is that they need to be loaded with buckshot, usually 00 is recommended. This is generally recommended by folks who are confused about the basic purpose of a home defense gun. Your objective shouldn't be to kill an intruder, but to stop them from hurting you or yours. Whether they die is entirely up to them. The ideal ammunition for this purpose is Field Load #6s, generally used for small game like rabbits. Filled with lead balls .11 in. in diameter (7/8 ounce in 20 gauge, 1 1/8 ounce in 12 gauge), this load is devastating at inside-the-house ranges, but in the event of a miss is unlikely to penetrate interior walls and endanger anyone in another room.
If an intruder ignores the warning provided by the pumping of a shotgun, do not argue with them or threaten them; shoot them where they are biggest and reload. If it appears there is any fight left in them reshoot them. You're not playing mumblypegs.
Storage of a firearm such that it is safe AND immediately available is a tricky proposition, but the pump shotgun is the easiest to accomplish this with. If stored with a full magazine tube and an empty chamber, in order to load and fire it one must simultaneously depress the slide release, located beside the trigger guard and pull back on the slide handle, then push the slide fully forward and release the safety. With a little practice this is easy for an adult to do but it's extremely difficult for any small child or two to pull off. Of course, it should still be stored where access is difficult for a child, such as a gun rack mounted fairly high on a wall.
If you have a child who cannot understand that some things are only for adults, or cannot learn that, you shouldn't have a gun.
For those with no experience or training with firearms learning to use a pump shotgun is easy, and any shop that can sell you a gun can put you in contact with someone willing to teach you. For lady Kossacks for whom cost is no obstacle I can offer personal instruction anywhere in the Continental U.S., just sing out in the Comments...
There are three basic, overlapping Rules that apply to ALL firearms; memorize them before even considering the purchase of a gun.
Treat every gun as a loaded gun! The FIRST thing you MUST do when picking up any gun is to open the action to visually inspect the chamber to determine if it's loaded. Very few people have ever been hurt by an empty gun, but lots have been hurt when somebody thought one was empty.
NEVER point a gun at ANYTHING you aren't willing to shoot! You would be amazed at how often this Rule is ignored, and later regretted. To stay in compliance with this Rule requires that you know AT ALL TIMES where any gun you hold is pointing.
Be sure of your target before firing! If there is ANYBODY who could legitimately be rummaging around your house at 3:00 in the morning, make sure you aren't shooting them by mistake. This is another strong point in favor of the pump shotgun over all other weapons; it always gets a reaction when pumped in a quiet house.