I'd say whatever you decide to start with is what you should use for a while. That way, you can figure things out consistently. I switched from hard to soft to medium rock and ended up destroying too much quality rock because I didn't have the basics down before I moved to the higher grade rock. I started by pressure flaking to understand platforms and abrading, then moved to billets.
Besides working local rhyolite, I bought buckets of Pedernales from Texas (which is slightly similar in hardness) and developed consistent billet flaking before I moved forward from there. Like most everyone else said, inexpensive is the way to go.
Jim