OK, I saw this and had to put in my $.02
First of all, I will begin by stating that there are few, if any, absolutes when it comes to selecting a firearm for defense. These are merely my thoughts.
I've carried a Beretta 92 (9x19mm) for 9 years now working for an Atlanta metro area county PD. In all that time I have never had a malf. When I took the advanced firearms course, we shot over 500 rounds apiece (maybe closer to 1000) in three days and I did not clean it once. I kept it lubricated, but left it dirty to see if it would pull through and it did. I've shot Glocks and SiGs. I liked the SiG, but did not like the feel of the Glock. Is it reliable? Yes. I personally did not care for it. I'm not adverse to polymers per se, but I like the feel of something really solid in my hand. I'll put it to you this way-whether I'm still working for PD or not, I will always have a Beretta somewhere. The other I recommend is the CZ-75. It's been the workhorse for Czech soldiers and police since...well...1975. It's available in numerous variations-full size, compact, tactical (and please don't let dealers sway you with that word), double action only, single action only, decock-only versions...you get the idea. Most can be had for $450-$550. CZ's are well-made and reliable. I have a CZ-83 (9x18mm Makarov-totally different animal from a 9x19) and have no qualms about leaving it for my wife while I work nights.
.40, .45, .357SIG...hmm. First of all you may hear people talk about "one shot stops." Bullshit. You can't rely on that. We train to do a double tap center mass. If they keep coming, you assume they are crazy, hopped up something really bad, or wearing a ballistic vest. Then you put one in the brain box. It was said earlier that shot placement is vital and that is absolutely true. A .22 to the chest is better than a miss by a .45. For the home, I think a 9x19 and up is fine. Anything smaller should be used with caution. Shotguns are effective (especially the racking sound-guaranteed to make any perp easily tracked by a K-9), but if you're doing a what-was-that-noise-honey-please-go-check-downstairs house clearing, the shotgun can be awkward to maneuver with without proper training. If your intention is to call 9-1-1 and wait in your room (nothing wrong with that, by the way) then it's perfect. Point it at the door and the shot spread will be most effective if someone comes through (but don't shoot the police, please).
If you have limited time or money for training, a revolver is a good bet. As was stated, you pull the trigger and if it fails to fire, pull it again and fire the next one. .38 special +P, .357 mag, or .44 special will work. You can also buy revolvers that use .45ACP rounds in clips that fit in the cylinder. I would get at least a 4" barrel. 2" barrels reduce muzzle velocity and increase recoil in addition to being less accurate if your aim is not dead on. One drawback to wheelguns is a longer reloading time. And there is less room for error since you have 5-7 rounds as opposed 10-15 (but rounds carried won't matter if your shot placement is good, right?). Admittedly, my revolver experience is limited.
No rifles for urban/suburban home defense. If you miss, it will likely go into your neighbor's home or even worse, hit one of your own.
No ported barrels. Ported barrels reduce recoil by directing gases upward into your line of sight. Bad news when your eyes are operating in darkness.
Don't carry more gun than you can handle. The longer it takes to recover from recoil, the longer it takes to get back on line for the next shot.
Buy a flashlight. A good one. Streamlight Stinger is my duty light. It will blind the suspect and ensure you are not about to pop off a loved one.
Practice, practice, practice. This cannot be stressed enough. No matter how good you think you are there will always be someone better.
Best of luck to you. It would appear that the board members are more than willing to answer any further questions you have. You know where to find us.
TampaSupremo