As advised to me by the Durham City Police Dept. in NC, use No. 4 Buck. It is small enough to reduce over-penetration inside the home yet powerful enough to ruin your day. It's spread is such that you increase the probability of hit(over 00) and... in a more morbide way, you aren't going to get fixed after taking a load of No. 4 Buck! They can't fix you after taking a shot of it, there's too much lead spread over too large an area for them to be able to put you back together.
However, No. 4 is expensive and hard to get, at least for me. So, Field loads such as 6 shot are very effective within typical room/hallway distances! Want to test it? Set up some pumkins or water melons at 10 yards and pepper 'em with 6 shot, you'll see. As stated here, slugs are less then ideal! Too much lead moving too damn fast for inside the home. 00 Buck is great and will do the job, but it may not be the best option.
NOTE: Yes, 7 & 8 shot within room distances is enough to ruin the hell out of the BG's day! At this distance, the wad hasn't seperated from the shot... you basically are shooting a frangible slug! However, once the distances gets to about 10 yards(depending on barrel) you have reduced the effectivness quite a bit. Will it still hurt? Hell yes it will... but it may not be enough to kill the BG. With that, it may still be enough to stop the BG... mission accomplished, no?