I use Tandy, Springfield and Weaver. It's going to depend more on the project and if it's for you or sale. I do leather work for fun and give away what I make or throw it in a box and move to the next project.
If your just starting out and want to learn nothing wrong with Tandy been using their leather for almost 40 years and have belts and holsters most people could not tell the difference between Tandy and Herman Oaks.
I do like Herman Oaks and it's definitely very good leather tools good again it's depends on what your doing.
Give Springfield Leather a call nice people to talk to and see what they have on sale.