Ninja Novus Weapon

[Nekodar]

If you're trying to plan for it, collect crit and det.
If it turns out other stats are more useful, those should still sell for more than other materia.

So you should instead concentrate on getting the oil for base relic, 3 mists for zenithing, 12 atma, make sure myth and sold are capped or near capped when 2.4 hits so you can start buying books asap, buy the 3 inks for novus scroll, and collect 75 alexandrites.

Or an UAT+Sand+10xRowena's Token (soldiery) for i110 weapon that you can use from the moment you hit 50 without going through relic quest.