Echoing Black Knight's post, the first gun I grab from my bedside Gunvault (I have an 18 mo old son) is a S&W 686 Plus loaded with the Remmington 38+P Lead SemiWadcutter Hollowpoints (aka, the "FBI Load"). Very good penetration with reliable expansion, and very low recoil in the heavy 686 makes for quick, easy follow-up shots. Don't understimate a good 38 Special with the right ammo. Success in a gunfight isn't about energy transfer or caliber. Mindset (software) is far more crucial. As someone else suggested, everyone should at least run through different scenarios in their mind, over and over. As for the gun, as long as the ammo achieves sufficient penetration (I go by the FBI's 12" minimum), is reliable and points naturally you should be good to go. Unless you have money coming out of your ears, be sure to check ammo prices. That can make a HUGE difference in how much you shoot. 9mm, 40 S&W and 38 Special are typically the least expensive center-fire rounds. 45 ACP and 357 Mag get a bit expensive, and 10 mm, 44 Mag and 45 Colt are "reloaders cartridges" for most of us regular folk due to their high cost.
My 686 may be the first gun I grab when I hear a bump in the night, but if I have time I'll get my 12 ga Mossie 590 from the closet, loaded with Federal Tacticle 2 3/4" 00 buckshot. Nothing stops badguys quite like 9 .33 caliber pellets hitting at nearly the same moment. Gives me a nice warm fuzzy to know that it is nearby
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BTW, you might want to read this Box 'O Truth article about 12 gauge penetration. Even with 00 buckshot, overpenetration is less of a concern than most pistol rounds.
http://www.theboxotruth.com/docs/bot3.htm
And for real God forbid, hurricane Katrine feces-hits-the-air circulation device moments, I have this in my safe loaded with 7.62 x 39 mm 122 grain JHPs: