I use pieced cotton fabric I think the wide backing fabric is all too boring. I like a backing to be completely different than the quilt top.

Cotton fabric, usually same weight and type which blends with the top. I like my binding to match both sides of the quilt.

It depends on the quilt. Baby and kids quilts get minky or flannel. A quilt that will be used for a comfy quilt, as a throw or sofa quilt, usually flannel, maybe minky. For a decorative quilt, I try to use quilter's cotton, something that somewhat coordinates but look for a sale or may have something in my stash. I prefer to have at least a little design on the back since I FMQ on my domestic sewing machine and like the quilting to blend into the back. I don't make show quilts so I don't think I need coordinating fabric from a particular line for backing. I love the look of using leftover blocks, etc. but so far have not been that creative. Maybe one day I will.

I try to use up my scraps on the back or extra blocks.

I regularly buy 100 cotton duvet cover sets from IKEA. They are a bit thinner than quilting fabric and do shrink by up to 5% but I just wash them first then starch. I can usually get 3 backs out of a set which I buy for around £15. They are usually good patterns on back and people comment on how nice the backs are.

Jane, love your hexie border.

I use left over fabric from the front, coordinating fabric from the stash,pieced Moda muslin, and occasionally buy wide backing fabric. Diane C.

If the quilt is one to use on a bed or a child's quilt, I choose something that is a pattern with eye appeal. If it's for a wall hanging and will not be commonly seen, I'm more inclined to pull out the muslin.

cgaraas
 

I use mostly flannel on backs of my quilts. I have made some baby ones with Minky. If I send it away to be quilted, then I use 100% cotton widebacks if I can find them on sale.

whatever you have! Leftovers from the front - great, fabric you are not sure why you bought - fine, sheets with lower thread count - terrific, a not too thin muslin you got at a great price - perfect, another top that you realize you don't have anyone to give it to - sounds good to me. In other words, there are no real hard rules.