Realistically?
I'll take a shield and a spiked mace.
The reason being that I know very little about swordsmanship, and "graceful" is not a word that would be used to describe me. However in goofing off I believe a shield gives a massive advantage and I'm pretty good at thumping people.
I'd still probably lose if my opponent knew anything about fighting with ancient weapons since I know very little, but the above would probably give me the best chance.
I think some people's choices are totally overlooking their real world capabilities. With no offense to anyone, but a game nerd is NOT going to lift a Katana (like Sepiroth's) that is as big as he is. Part of what makes that fantasy is that nobody could wield a weapon like that the way he does, especially if they were built like him (or inferior). I doubt most of the champions of "World's Strongest Man" competitions could use that weapon anything like in the games.
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Also for the record if I knew anything about swordsmanship I would pick a US calvary sabre circa the late 1800s. A guy who does handle weapons like that apparently (Robert Adams, who wrote things like "Horseclans") at one point went into the pros and cons of differant swords and mentioned that one as being the best sword overall.
The bottom line is that technology increases given time, and swordsmithing and weapon designs continue to progress based on what was learned in previous generations of weapons. Longswords, Rapiers, Katanas, Kopeshes, etc... all were very good in their time periods and dominated their neck of the woods, but the last generation of real swordsmanship (when it was truely dying) learned from all of those developments. That paticular style of sword pretty much has all the advantages of previous generations of weapons including a curved edge, sharp point, and perhaps the best compromise in terms of a weight to strength ratio. They are also designed to be used both on foot, and on the ground, and are long enough where they can be used to charge on horseback (albeit they aren't lances).
I'd imagine that if someone how I was training with swords that's the same one I'd pick given the arguements I've heard in it's favor.
Incidently advances in armament are also one of the big reasons why a lot of recreationist groups can be so anal when it comes to keeping things "period". If you have a bunch of dudes fighting with weapons a time period is usually specified, if some guy with equal skill shows up with a weapon that benefitted from another hundred years of weapon development he's going to have an unfair advantage.