#4 buck in 2-3/4" if you can find it - it's a nearly ideal round for home defence. If you have long hallways, look for it to be "buffered" - where the use ground polystyrene, sawdust, or something similar. The "buffering" works well for keeping the pattern under control (anything to fill the gaps well will work - I have handloaded 12ga shot loads (large shot!) and dripped paraffin from a candle into the spaces between pellets. Stack in layers, and drip molten wax in between for a solid column. The buffering blasts loose shortly after the charge exits the muzzle (even parrafin!) and leaves you with a tighter pattern.
How does it work? Easy - by filling the spaces between the pellets, you prevent them bouncing against each other. You also help prevent the pellets deforming when they bounce, allowing them to fly true.
FFZ