There are so many types and finishes out there. For me, it’s usually veg tan leather. The thickness really allows for some muscle involved in the crafting. And, it’s strong, so the finished good or item is usually durable.
Also, with untreated veg tan leather, over time normal everyday use will help give it a nice patina, so it gets better with age. I’m a big fan, and for now, it’s my favorite.