Imposing a totally arbitrary limit on myself, if I was picking a real weapon from some point in history, I'd go with either an Épée from 1600-1750 France, or a Ninjato from Medieval Japan, just because I'm a pansy and, if in a fight to the death, I want something light and really deadly.
With fantasy stuff thrown in, I don't think you can beat an Infinity Plus One Sword from your average fantasy story.
Although, Charlemagne or Julius Caesar's swords would be awesome to own as well.