In my opinion, one of the best kept secrets for a home defense shotgun is the 20 gauge Remington Express Jr with a Youth stock, 18.5" barrel, 12 inch length of pull. It has an overall length of only 37 inches and weighs under 6 lbs. This guns is particularly useful for anyone who might be recoil sensitive or for smaller framed ladies or young teens in the home who may be forced to use the shotgun for self defense if dad is not home. The recoil from the 20 gauge is 40% to 45% LESS than from a similarly equipped 12 gauge, but for home defense distances, using 2¾" #3 buckshot, it is just as deadly.
Studies have shown that it is much easier for a large individual to get used to shooting a smaller gun than for a small person to be able to shoot a larger gun.
You can easily find 2¾" #3 buckshot and even 3" #2 buckshot is available. If you want to spend the money, you can even get Tactical 20 Gauge 2¾" #00 buck shot from Paraklese Technologies.
Paraklese Technologies 20 gauge 00 Buckshot
Here is what I would recommend for home defense:
Pump Action Shotguns - Model 870 Express Jr - Special Run Shotgun - Remington Shotguns
I have used this same shotgun at the range as well as while hunting and compared to shooting a 12 gauge, the little 20 gauge is much easier to maneuver and actually a pleasure to shoot, especially if you are wearing a coat to further reduce the felt recoil on the shoulder.
You can often find these little jewels on sale at Dunham's or Gander Mountain for under $300 and quite often, Remington will also give you a $30 mail-in rebate.
Here is an excellent article by Massad Ayoob explaining why he recommends a 20 gauge shotgun for most uses especially for home defense.
Consider the 20-gauge shotgun by Massad Ayoob Issue #120
You can get an 18.5" rifled barrel with cantilever scope mount for it and end up with a sweet deer gun.
I can personally attest to the lethality of 20 gauge sabot slugs on whitetail deer at distances of 97 yards and beyond.
Below are a couple of excellent ProArms Podcasts Produced by Gail Pepin and featuring John and Terri Strayer, Massad Ayoob, Herman Gunter and other shotgun experts. Each podcast is almost one hour long, but well worth the time to listen to them.
A lot of good information here.
017A Homing in on the Defensive Shotgun
017A Homing in on the Defensive Shotgun The ProArms Podcast
017B Homing in on the Defensive Shotgun
017B Homing in on the Defensive Shotgun The ProArms Podcast