I've never fired an AR inside a house, but I can imagine if you did it without ear protection you are looking at permanent hearing loss. The big problem with a shotgun, large caliber pistol or something like .308 is overpenetration. They will go through drywall like it's wet tissue paper. Another downside with a pistol is the prospect that intruders might be wearing soft body armor. There is no perfect solution for all situations. Like CO said, a shotgun or big bore pistol is probably best for in the home, the AR for anything outside. A lot of gun guys seem to like the High Point carbine, which fires 9 mil or .45. Only has a 9 shot mag though as i recall. Very inexpensive and apparently pretty darn reliable. The S&W M&P AR seems to get good ratings for a budget gun. People get kind of crazy spending money on Ar's, but if you want mil-spec, a Colt is decent value.
I have this in 9mm. 10-shot mag, but you can buy a stock clip which holds 2 extra mags. Shoots great within pistol round range. Available at Cabelas for $349... where it gets 4.7/5 average from 78 reviewers. IOW... almost everyone who shoots one likes it.
I'm thinking seriously about getting one. Would you get another 9 or go for the .45? I am leaning to the 9 because of ammo costs, plus I have begun to have doubts that .45 has any real advantage in stopping power.
I've thought about getting another. I'd probably get another 9mm. The stopping power difference between 9 vs. .45 isn't as big as most people envision. Recalling from memory, the muzzle energy from a 9mm (4" barrel") is about 340 ft/lbs. About 405 ft/lbs from a .45. The 9mm fired from a 16" barrel carbine is about 500 ft/lbs. All of the Hi-Points are rated for +P rounds. (FWIW... the muzzle energy of the Henry 357 Magnum carbine can be close to 1,000 ft/lbs. An AR15, 20" barrel, 55gr, = ~1,300 ft/lbs muzzle energy.)
For home defense: Remington 870, with 00 buck For personal defense (concealed carry): Glock 43, with JHP AR15 for whatever: LaRue Tactical PredatAR 5.56
Forgot to mention... Henry also has a .44 Magnum carbine... muzzle energy ~1,400 ft/lbs! Magnum carbines don't have the reach of high-powered hunting rifles, of course, but have a lot of power within range.
While my preference is a .45 a 9 is something that you can get more practice with simply from a cost factor. Practice matters, because at the end of the day "stopping power" has more to do with accuracy than anything else.
Another pistol-caliber carbine option you might take a look at is the Kel-Tec Sub2000 which is very popular and has been around for more than a dozen years. A couple of advantages over the Browning is that it only weighs 4 lbs, folds in half for easy concealment and storage (see picture at link), and can be gotten in various configurations (ie, Glock, Beretta, SIG) to take regular pistol mags. That's a real convenience to share mags with your handgun and not be limited to 10rd.
Here's a place you might pick one up for ~$300-ish, after shipping and FFL transfer handling fee. I haven't seen these on sale at Cabelas, so their regular price of $349 + Tax = ~$380. Cabelas, however, includes the folding front-post grip... which I like. The grip is a $25 option. Considering the price, accuracy and reliability of Hi-Point carbines, I can't see how anyone can justify saying, "they aren't worth the money". And if you can find one used for $200, so much the better. http://www.gunbroker.com/Auction/ViewItem.aspx?Item=483508126