I agree that for home defense, the correct load is buckshot.
Anything powerful enough to kill a two legged varmint will be powerful enough to penetrate a typical house wall if shot directly into the wall.
For home defense I use #4 Buckshot in a 12 ga. or #3 Buckshot in a 20 ga. Both have good penetration within the distances found inside a home or apartment and are less likely to over penetrate as long as you aim correctly and hit your intended target.
Birdshot will make a very ugly but SHALLOW wound that may not penetrate the rib cage and is not recommended for anything larger than, well, birds.