I think of the back as part of the quilt design, so it needs to be harmonious and complement the top. I love seeing what people have chosen for their quilt backs. I only bought a wide backing once, and found it difficult to work with so I prefer piecing my backs from a regular width fabric. It's fun looking through the clearance items on Etsy for backs, and I also enjoy shopping for backing at Brooklyn Fabric, which sells for $8/yd. and they have a very pleasant-to-use website with a 'by color' search engine.