Since I do mostly handquilting I prefer solid colors and or muslin. If I can get it at a reasonable price I buy the wide stuff so I don't have to piece. I always judge by the feel of the fabric as I will have to handle it constantly. I like a plain back because it shows off my handquilting. I often check it to be sure I have quilted all of the parts of the top. It is harder to see the quilting because of the pattern or patterns on the top. I always shop for cotton fabrics in at least six yard cuts when Joann's has their 50% of discontinued fabrics etc. I have several tubs of various fabrics for backings in my stash. Each selection is at least 6 yards. As a handquilter I don't need quite as much fabric for the back as someone who will be using a longarm machine.