Tandy has been great for me- it got me into the hobby. I wanted to try it, didn't want to risk a lot of money if it turned out I didn't want to really get into it. I bought the $50 starter set, got a sink cutout from a countertop place and made an awl out of an old wooden rake handle. That was enough to get me started and realize I wanted to do more, so as I've needed more things I spent a little more and bought nicer stuff.
My go-to now is Sheridan Leather. I've had the chance to visit twice in person (went by today, actually) and the folks there are very knowledgable, have an absolutely astonishing selection and are really patient with my beginner questions. Went in today to ask about a way to fasten something I wasnt sure about, the gentleman not only knew exactly what I needed but opened a package of rivets, got a small piece of leather and showed me exactly what the finished joint would look like. I bought my nice (not made of a rake handle) stitching awl there about a month ago, and hopefully this winter I'll be able to visit them again for materials and tools to work on some bigger projects. I need a maul (still using the cheesy wooden mallet from the Tandy kit), and want to make some chinks.
Tandy made it easy for me to get started and there's a store in town if I need something today, but for the most part I think I'm serious enough about the hobby now to invest in some higher end equipment. I wouldn't be here if not for them though.