Gotta be Masamune. Xcalibur (sometimes spelled properly as excalibur) comes close, but speaking in pure damage terms (which, for the masamune, means a whole heck of a lot!
), plus ease of use (in most games, anyone can use masamune. Thats one of the things thats so great about it), Masamune is definately top.
Edit: oops, saw that Fantasy was capitalized, and my mind automatically added Final.
guess I've been playing a little much FF. I'd still say Masamune, however.