I wouldn't use a 12 gauge slug for home defense (esp in an urban or suburban environment). I like #4 buck for close quarters defense, esp inside the home. In my experience, the Federal #4 buck mini shells pattern tight (tighter than the regular 2 3/4" #4 buck loads in my experience). I would feel very confident using them within 15 yards, you also get increased magazine capacity, less recoil, and less muzzle blast / flash indoors. 15 pellets of #4 buck in a 12 gauge mini shell is very comparable in power and payload to non magnum 20 gauge buckshot loads.
Standard buckshot loads work too, though I'd adjust the pellet size depending on the specific conditions (urban vs rural, kids / others in the home, etc). I'm also a fan of heavy birdshot for close in (under 10 yards) urban / hotel / apartment defense. ATI has a nice standard pressure 2 3/4" load of one ounce of lead BBs (more energy than steel). I guarantee that within 7 yards, even from a cylinder bore, that will stop any unarmed 2 legged threat with greatly decreased risk of penetration through walls, etc. IF your shotgun has the ability to accept chokes, then it's that much more devastating with a full+ constriction (with even greater effective range). Of course standard #4 buck works great too, as does 00 if over penetration is less of a concern.