I believe Dragonscale is the best option. Be careful though, cause even after you choose, you'll never be able to choose a different type of leatherworking on that toon (yes, even if you drop it and level it again).
I know Elemental is for Rogue, and I would think Tribal sounds like Druid, but you may want to check actual Dragonscale recipes to be sure that's what you want.