I used muslin on one quilt only. I usually coordinate. I also jazz up my backings by adding my leftovers to the back. Sometimes I just coordinate. I took a class on
www.craftsy.com on quilt backings, for free, and have used her method a few times and like it. It has to go with the front of the quilt though. And I'm into modern quilts right this minute now, so her method is what is working for me. I say "right this minute" because I can change my mind the minute I see a quilt I just love and have to make.
But I'm taking her Modern Quilts class on Craftsy and love how she does modern quilting. I'm not into artsy quilts yet. Just modern looking ones. The ones where all the blocks are in one corner and there is blank space with solid fabric in the rest of the area. I just really think it's catchy looking. Try her free backing class. It'll introduce you to her and her style of teaching and her modern quilting. It's free. What can it hurt? It's a free video.