As for home defence ammo, I would recommend buck shot. I use 00 in a 3 inch shell that has 15 pellets. Really any buck shot size will work but I would go to much smaller then #1. But to each his own.
As for bird shot, its name says it all. It's for use on birds, not some one threatening you life. Bird shot does not penetrate enough to be consitantly effect.
Slugs will put anyone down, but penetrate alot and if you have loved ones in the house it can be dangerous. Hope this helps.