A sword is not particularly good when faced with a ranged opponent. You'd want a bow of some sort, depending on how fucked up thinngs were (i.e. are somewhat advanced materials still available), you'd go with a compound bow, or more primative, a horn bow or longbow. It would largely depend on the circumstances though. Are we talking about a Mad Max style collapse, where there is still some sort of functioning technology and you're going to be defending yourself against criminal thugs? Or is it something more like The Road, where it's just you versus what's left of nature. It's likely that no single weapon would be suitable for all circumstances. You certainly wouldn't find a weapon that would be as versatile as a self defense weapon as a hand gun is.