Generally Grand Weapons. There's a couple gacha weapons that are also comparable or better but generally assuming you plan on going primal in any element you'd want to get 2 or 3 grand/normal mod weapons to start with. For Dark that'd be Pain and Suffering and Fediel's axe, for Light that'd be Two harmonia and either an Eden or a Nehan harp (or else 3 Eden's), for Earth because we run Caim 99% of the time in the back its pretty much just pick whatever but usually Cain's katana, and then just two others really hard to go wrong here.
Wind: Unless you have multiple copies of Halloween Vane and or Sho's weapons don't bother, same for Fire.
Water depends on what you want to do but honestly you'll be running a lot of free weapons anyway between Wamdus' spear, Dark Thrashers, the Kris, and Colomba so only ones I'd really say are must haves to do would probably be Grand Lancelot's dagger for skill setups and Poseidon's trident.
