It completely depends on the quilt and the quilt's ultimate use as well as if I have ample time. I seem to like peiced backings and wide (108") fabrics equally when it comes to backing. I do have some stash of wide muslin and a couple of neutral wides that I turn to fairly regularly and a few pieces of wide batik that I am saving for something special down the road, but what that something special is, hasn't even been conceived of yet, let alone made. I don't tend to buy wide backing for a specific quilt (but I have on a couple of occasions). If I need more wide back fabric I will buy enough of it to do several quilts in a neutral color. If I have time and inclination I will piece a scrap quilt for a backing that may or may not have fabrics from the front. I like doing pieced backings because it 1. Helps me deplete my scraps and 2. Gives me a two for one double sided quilts and 3 I love to piece so I get more peicing in.