Here's a link where they concluded that in a 12-gauge shotgun, No. 1 buckshot was the best all-around for home defense:
http://www.firearmstactical.com/briefs10.htm
Unfortunately, No. 1 buckshot is hard to find, so the next recommendation was plain old No. 00 buckshot.
Good article. I used to love to shoot slugs at an old washing machine. Have plenty of buckshot on hand also.