I love wide backings. I look around to see who has the best prices at the time for the top I have finished. Marshall's Dry Goods usually has a great selection and good prices. I have not had a problem with the quality of the fabrics either.
I rarely piece together a backing. I have one now that has entered my UFO box because I just can't get it right. It is pieced.
There are a number of options available for backing fabrics. I believe the backing is as important as the top so quality and proper fit are important to me.