I'm glad folks brought up the smaller loads, saved me a lot of typing. Will throw in my two cents worth and hopefully not parrot any one of the above too much.
Generally speaking you want a form of bird load for home defense, at least for your first one or two shots. Our department personnel who teach civilian firearms courses recommend straight bird shot for home defense; 00-Buck and rifled slugs are great for LE, but not always appropriate for the home. Birdshot will give an adequate spread that hopefully will find the target on your first "point and click" instinct (well, hopefully not "click" - "boom" is preferable here but I digress). Added benefits to this approach as noted above are wider effective area, especially at distance, and minimal damage to what lies in and beyond your walls.
When deciding how to load your shotgun, keep in mind your home defense circumstances. If your round penetrates the wall and keeps going, what or who might it hit (gas lines/appliances, children's bedrooms, or neighbors if in multi-unit housing)? Do you have thick (i.e. concrete / rock) walls, or thin walls (i.e. mobile home)? Next look at the ballistics and load the biggest bird load you can find as your first round (and second if you so choose). Follow up with any progressive scheme you like, there are some good examples above. Round or two of smaller Buck, some 00-Buck, maybe even a couple slugs. My work SG's loaded straight 00-Buck with Slugs on the stock. My home SG's loaded (1) #6, (1) #4, (3) 00-Buck, (2) Slugs.
Another thing I'd like to suggest is investing in a good light system for your home defense gun. Middle of the night, adrenaline-induced accidents can be significantly reduced by proper target identification. Please shoot criminals responsibly
. All joking aside, I would also like to clarify that shooting for trespassing exclusively is NOT covered under justifiable homicide, at least not in any state's statutes I'm familiar with. The things to keep in mind, in order, are as follows: (1) 'Tis better to be tried by 12 than carried by 6; (2) If you shoot someone, you *will* to go jail until its all sorted out; (3) If being tried by 12, you will be judged on whether you had reasonable and justifiable fear of great bodily injury to self or others, and whether a reasonable person in your situation would have had that same fear and would have acted in the same way.
Adhering to these guidelines will keep you and your loved ones alive and free so that the family can come after everything you have that their perfect little angel wasn't able to steal from you.