When I buy fat quarters, I buy them individually. I don't like other people picking out my material for me. I'm making a quilt with different colored stars in it for my daughter. I had a lot of fun picking out the fat quarters for the individual stars.
After saying that, I have to admit that most of the time I buy my material by the yard. I always buy 1/4 or 1/2 yard more than I need so I've built up quite a bit of stash of my own brand of fat quarters. What I've bought at different times in the past, coordinate very well together when I mix them together for my present or future projects.