I agree with Kawaii, the FF6 Sword on the cover.

But as a unique FF sword I think the Blood Sword which has appeared in many games is a decent one to represent the series. Or perhaps the Excalibur(but thats stolen from King Arthur not a FF original).

The Sword is most definitely the weapon in my eyes that represents any medival style RPG that most FF games are. Only 8 really is in a 'modern' world and they still use the medival technology in weapons. Come on, a whip? No one uses whips anymore.

If I were to showcase FF to a newgie, I'd show them FF6 because its essentially your standard FF game, in its best form. Lerge group of pwople together to fight one bad guy. They learn magic and use various weapons.

Here's a question you can answer if you like. Which character most personifies Final Fantasy?