Shotguns are the best choice for an "Only" Gun.

[Skinny Shooter]

Adam I agree with your thoughts.
I only use 00 Buck in my 12ga.
This website has done some interesting tests:
http://www.theboxotruth.com/docs/bot3.htm

The following is why I won't use something smaller.
Birdshot might work if you pop someone in the head at extreme close range but who can do that in the dark at 3am after waking up from a deep sleep?
Besides, Dick Cheney is still walking as a free man...

http://www.ar15.com/content/page.html?id=176

Some hollow point pistol bullets may fill up with clothing fibers and fail to expand. Someone shot with birdshot while wearing heavy clothing and/or is high on whatever, might just shrug it off and then kill you.

Allen