flour for sourdough
If you're looking for flour to make starter, most flour will do. But freshly ground rye flour is one of the best for that purpose. If you want to know which type of flour makes better sourdough bread, I would say whatever type of flour you like the most will be the best.
I don't know anything about "best for bread". Is that some type of bread flour? Bread flour is designed for lighter and softer texture.Why don't you get some whole wheat and mix it with some white flour or unbleached to see if you can get the same result?
I used rye, whole wheat, and unbleached flour to make different types of bread. Each flour has its own distinct flavor and the end products texture and volume will be different as well. If you like the heavier texture of whole wheat bread yet a bit volume, use 70 - 80% WW then the rest unbleached/white/bread flour. If you like strong flavor rye will do very well. For my regular sourdough bread I use a mix of whole wheat and unbleached flour. But I use rye to mix with whole wheat to make Russian black bread for hubby and little man because they like strong flavored bread. When I make sourdough garlic bread mostly unbleached flour to give the right texture. It's all about your taste and experience.
Once you have your sourdough starter ready, the possibilities are endless. Just experiment and have fun with it.