I almost always purchase a wide back there is such a great variety available now. Fabric.com has a huge selection, so does backside fabrics. That being said, often I choose something that will compliment the top. Something that will look good with the binding I plan to use and I take into consideration what thread color I plan to quilt with. Very seldom do I use a solid, once in a while, even white I tend to choose a white on white print of some sort that is complimentary to the top.