My vote is definitely for Buckshot. Which type and size is a decision that should be considered in light of your particular situation. For me, I use #000 in my pumps and 2 3/4" magnum (20 pellet) #1s in my Benelli autos...but...I live alone except for my dogs and am in a home on a large lot in a residential subdivision where it is very unlikely that any shot from inside my home would exit and enter another house. (Not an impossibility, but pretty unlikely)

If I had a wife and kids at home, spread out in several bedrooms, or, maybe lived in an apartment, etc. those circumstances would effect my choice of ammo...at least for the first couple of rounds. There I would most likely compromise by loading some of my hoarded "Q" load WW #4 Buck (hardened pellets) for the first two rounds at least, and finish with #000...can you tell I like #000? Realize that even #4 Buck can, and will, penetrate standard drywall construction...it is all a trade-off.

As an LEO, for all-around LE response shotgun, I usually loaded so that my first three or four rounds (depending on the gun) were #00 Buck (issue) and the last two were slugs...mostly using an 870 with one shot extension / empty chamber...sometimes an 870 with two shot extension...on the theory that after I had fired several rounds of Buck there was a good liklihood that anyone who still wanted to fight was behind cover.

The above is predicated on using the gun inside the house...not on stepping out the door and engaging the BG outside...there I just might want a couple of slugs available, but frankly would be more inclined to use my M4 with SF light and Aimpoint, assuming I had time to grab it from its "New York Reload" position next to my 870!

JMO

Federal Ruduced Tactical 00 buck