Usually what they have to offer, sometimes prices. If I have seen a fabric that I really love I usually check out the LQS by vieing on their website and sometimes calling before I drive anywhere due to the cost of gas. I don't mind driving there if they have what I want/need (usually want). If no one local has it I go online looking. There are a couple of shops that I know what they carry such as Moona Fabrics has more modern fabric lines (Art Gallery, Amy Butler looking fabrics) and because their prices are so good if that is what I am looking for I go there first. I would say it is a combination of choices and prices. I do try to support some of the local shops, especially those that go out of their way with opening up classrooms for free sew days and things like that.