Jewelry or Cooking, as they don’t consume the same craft mats as armorsmithing. If you decide to level up both professions, they won’t be wrestling each other for the same mats(Jeweler will need both copper and platinum which Asmith also uses, but that’s it).
If you only want to level up one at a time then I would pick whichever profession crafts the 1 weapon you use the most.