My opinion- for home defence: and only if you're willing to practice marksmanship, get a little training, and maintain the fire arm.
Hand guns: J or K frame Smith and Wesson revolvers in .38 special , 4"bbl minimum. The Tarus clones are ok too. Unless you are willing to practice, the 2" snubs are a little hard to shoot consistently. .38 special is around a 70-80% one shot stopper in most common loadings and ammo is cheap enough to encourage practice time at the range. Revolvers in general are very reliable and simple to operate. Smith and Wesson and Colt revolvers are reasonably priced, especially on the used market. Stainless steel ( a few bucks more) holds up to the elements without the attention a blued finish requires.
Autos- ignore the "cool factor" of auto pistols unless you are into taking care of your weapons. Auto's have tight tolerances and will not function properly unless clean and lubed. Autos can be hard to use under stress unless you are totally in practice with the safety and other contols. Auto pistols can not be considered "reliable" for combat situations unless they are broken in- usually 500 to a 1000 rounds fired without malfunction will test a auto to my satisfaction before I will rely on the weapon for defense.
Calibers: .38 special, minimum. .380 is ok as a back - up in trained hands -a little anemic and the auto pistols chambered for it need regular cleaning ( a little grit in the tight actions will jam them up). 9mm has comparable ballistics in many loadings as the .38 special. If you're willing to work at marksmanship .40 S&W and the venerable .45 ACP are excellent choices. .22 and .25 auto- forget it. Those little guys are for blasting tin cans ( or mob hits).
High Capacity- it's lots of fun blasting off 13 or more rounds in rapid fire semi autos. However, most gunfights are less than 3 or 4 shots between both shooters. Most gunplay is at distances less than 30'.(from an old FBI study)
I have never felt under-armed with my .38 special, 5 -shot J frame S&W yet. I do prefer the "warm and fuzzy feelings" I get when armed with my trusty full- sized Government Model Colt .45.
Shotguns: If you don't wish to invest the time and practice to become a good handgun shooter the Shotgun is a good choice. Any shot gun will do. Shotguns loaded with low brass, #6 or 8 shot limit the hazzards of over-penetration in wall board homes. Pump action shotguns are very reliable and easy to learn to operate. In my experience the sound of a pump gun "rackin one in" will un-nerve all but the most dedicated bad guy. That noise gets folks attention and looking down that big bore is pretty nerve racking.
One last thing- if you are WILLING to present a firearm in self Defense you must be WILLING to TAKE A LIFE! Get some professional training from a NRA certified trainer and learn your state laws. Being able to defend ones self is gratifying but a grave responsibility.