Handguns are the most popular firearms for home defense. A pistol is handy indoors and can be conveniently concealed almost anywhere in the home, ready for use. It is the easiest of all guns to retain in a hand to hand struggle. It can be fired from either hand in an emergency situation. (This is especially true of revolvers). Centerfire pistols and revolvers from approximately 9mm/.38 caliber on up, assuming appropriate ammunition is chosen, offer good stopping power for indoor home defense without the extreme risk of over penetration of a deer rifle. They are much less likely to severely damage the home you are trying to protect than a shotgun. For all of these reasons handguns are the first choice of the majority of experts for home defense.
Of the various types of handguns, only revolvers and autoloading pistols should be considered for home defense. Service or concealed carry type handguns are the typical choices. Deep concealment pistols ("mouse guns") are not a good choice for home defense. Why handicap yourself when better guns for the purpose are readily available?
Because a home defense gun does not normally need to be carried on the person (and if it does an exposed holster and gun belt can be employed), I tend to favor the service type handgun for home defense. These usually come with better sights and are easier to shoot accurately than the smaller, lighter handguns designed primarily for concealed carry.
Autoloaders, or semi-automatic pistols, are the choice of the world's military services and the issue weapon of most police forces. Modern examples of service style autoloaders include the Beretta M92 series, Ruger P series, SIG P229 and P239, and the Full-Size and Compact Glock pistols. All of these are double action or safe action pistols that can be safely stored with the chamber loaded and the safety (if present) off. If the whistle blows it is not necessary to manually cycle the action or manipulate a safety, just pull the trigger and the gun will fire. In this they are much like a double action revolver.
Autoloaders hold more cartridges than the ordinary revolver, typically about 10 rounds, and are faster to reload if a pre-loaded magazine is handy. However, autoloaders are very slow to reload from a box of loose cartridges--the situation that usually pertains if a homeowner shoots his or her pistol empty. An autoloader can deliver very rapid fire, but remember that you can't miss fast enough to win a gunfight. Unlike the characters in the movies, you have to take the time to aim if you are to successfully defend your home!
Autoloading pistols are more likely to jam than a revolver, particularly if fired through cloth, say from under a bathrobe in a sudden emergency, from an unusual orientation (upside down for instance), or with a "limp wrist" (insecure hold). They have one other very significant drawback: they are magazine fed and the spring in a loaded magazine is tightly compressed. Magazines should be rotated on, at least, a monthly basis. The spring in a loaded magazine left unattended for an extended period of time may take a "set" and then lack the pressure to reliably feed cartridges, causing a jam.
A high quality autoloader, owned and maintained by an experienced shooter, is a very good home defense weapon. It is perhaps not so good for the casual user who is not a recreational shooter.
Our top choice for a home defense gun is a revolver. Revolvers usually hold six cartridges, but some hold more. Revolvers are ambidextrous. Perhaps best of all, they can sit fully loaded and untouched for decades, as all springs are normally at rest, and still be ready to go into service at a moment's notice. Just grab the gun and commence firing should the need arise. Medium size revolvers, the kind I usually favor for home defense, come in two action styles, single action and double action.
Single action revolvers
The single action (SA) revolver must be manually cocked before the trigger will fire the weapon. These are the traditional "western" style guns, such as the Colt Single Action Army and Ruger Blackhawk and Vaquero models. Such guns are slow to reload, but powerful, accurate and deadly when the whistle blows. Their "plowhandle" grip shape fits most hands exceedingly well, making accurate fire comparatively easy. They can be fired rapidly from a two handed hold by cocking the piece with the thumb of the off hand. Never "fan" a single action revolver!
Somewhat like autoloading pistols, I regard SA revolvers as an entirely satisfactory choice for home defense, particularly for experienced shooters, but not the very best choice for the casual user.
Double action revolvers
The all-around best choice among handguns for home defense is the double action (DA) revolver. These are the typical "police" style revolvers, such as the Colt Python, Ruger GP100, or the Smith and Wesson Model 10 Military and Police. Double action revolvers may be thumb cocked, just like a single action revolver, and then fired by a light pressure on the trigger. This is generally referred to as shooting "single action," and it is the most accurate way to deliver aimed fire. They may also be fired by a single long pull on the trigger, which first cocks and then releases the hammer (trigger cocking or "double action" shooting).
Trigger cocking requires a longer and much heavier trigger pull, but it is fast. Shots can be delivered as rapidly as from an autoloading pistol. It is sufficiently accurate for close range shooting (out to perhaps 7 yards) in trained hands.
Double action revolvers are very safe, simple to operate, relatively easy to shoot accurately, very reliable, and extremely difficult to jam. They can be reloaded quickly if a speed loader is employed, and are very easy to reload from a box of loose cartridges should that become necessary. For the average homeowner as well as the expert pistolero, a DA revolver is hard to beat for home defense.
Whatever gun is chosen for home defense, become familiar with it. Make it a point to practice at reasonable intervals. A handgun can potentially save your life and the lives of your family. But it isn't the weapon per-se that gets the job done, it is the person behind it. Skill and determination, reinforced by regular practice, will carry the day. Remember that, as Bill Jordan pointed out, there is no second place winner in a gunfight.