To answer the question posed: Anything that gets the job done. I'm now thinking about a katana for home defense... actually just kidding.
This brings up an issue that has bothered me for a while. Just this week, Plaxico Burress started serving a two year sentence for the privilege of shooting himself in the leg. While I understand that the Glock in the gym pants waist band isn't a way to violate the abject stupidity of New York gun laws, it brings into focus a problem that has reared its ugly head several times for NFL players. For the most part, professional football players are large, in-shape, intimidating type people. They, however, are not bullet proof. To bring it full circle, Sean Taylor was shot and killed in his home using a blade for home defense. He had gotten into trouble a couple of years earlier with an incident involving a hand gun. IMHO he died so that the "evil gun" could maintain its place as one of the most demonized and mis-represented inanimate objects ever to share space with humans.
So, blades are nice, but a 200+ grain piece of metal launcher is always better.
P.S. For those of you who are unfamiliar with who Sean Taylor is, I have included a video (albeit a crappy one) of the man's competitiveness at a meaningless game in Hawaii.
http://www.youtube.com/watch?v=SF4QJwfKaeU&NR=1Rant and thread hijack off.