Heavy 9-10 oz vegetable tanned leather is what you want. I don't know if most leather makers say what their leather is but no maker of quality leather goods will use anything but vegetable tanned. As for other tanning processes there's urine tanned. A lot of Mexican leather is tanned that way. It's good leather and is usually heavily embossed and it's super cheap. Just don't get it wet or everybody around you will think you peed your pants.
When it comes to leather you usually get what you pay for and quality leather isn't cheap.
This is my current rig made by Brazos Jack of Etowah River Leather. It's about a 400 dollar rig which is pretty cheap for custom leather. It's a Mexican double loop copied from an original.