And why?
To me, is a tie between Astrolabes and Rapiers. Both are usually very good looking, and I really like how the jobs actually use them in combat, especially Red Mages when their casting stance kind attaching the focus to the hilt makes the weapon resemble a staff.
Bonus for the worst weapon:As much as I love SMN, I can't be excited for books whenever there's a new weapon collection out. They're usually either too boring or have way too many attached junk add-ons. There's only a handful of outliers that are actually really good and that's just because of the special effects built in.
I'd be more excited for them if the books, in general, had a simple design, but always came with some sort of aura, or sigil when they're open in combat.