[Jack]

I'll vote for a load of 7 1/2's out of a pump shotgun.
For one thing, the distinctive noise of a pump being racked will scare off any sane intruder.
At in house ranges, a load of 7 1/2's will hit like a slug, and leave a bunch of pellets to be picked out of the carcass.
But, Tater wants a recommedation for 357 or what? 40 S&W?
In a handgun, I'd lean towards a light for caliber expanding bullet as something that might not penetrate 3 apartments.
I think Adam's advice (don't miss) is crucial.
One thing to remember: after you fire the first round in the dark, you will be totally blind from the flash, so repeat shots aren't as much use as you think.