Most times I purchase my regular-width backing fabric when I'm purchasing the top fabrics. I usually end up using coordinating, relatively small scale prints. But the last quilt I did was for a HS graduation gift. The top was a softball field using all green; brown; tan batiks. I wanted to try to get the HS colors into the backing and ended up finding a fabulous fabric which incorporated all the colors from the top as well as the school colors I wanted. Stunning fabric.

My preference, whether using wide back or pieced backing, is for it to coordinate in some way with the top. I use "coordinate" quite loosely - it may be from the same line, but more often is not. If the top is predominantly blue, I'll use a blue print.

When I find great deals on fabric, usually clearance, I'll buy several yards with the intention for them to be used as backing. Sometimes I've done large pieces of leftover fabric, but not usually. Don't know why, I don't care for muslin or solid; I like the way a print looks. Living where I do, I am fortunate to be able to buy wide backs for the price that many folks have to pay for regular yardage.

I usually wait until the top is finished before figuring out backing. Most often I take the finished top to the LQS to choose the backing. My stash is predominantly smaller pieces so I can't 'shop' for backing at home. If I'm making the top from a coordinated fabric line, I sometimes buy a backing from the same line at the outset. I like both pieced and single fabric backings, depending on the quilt. I also love the look of a plain muslin backing, when appropriate. The stitching shows up so nicely on a solid back.

Once the quilt top is finished it usually comes as a complete surprise to me that it needs a back too. You would think I would know by now. I am really trying to pare down my stash, so I try to make the back from leftovers from the top plus anything else that works well. If it weren't for the too-large stash, I would prefer to just buy a wide back for each quilt, and then I could get along with quilting it and then making another top.

well when using plain color or muslin on the back the quilting shows up more so I like that so it does depend on how I will be quilting it .

I piece a lot of backings and like to use up the larger remaining chunks that were in the front of my quilt plus something coordinating.

Widebacks are the easiest to work with I think. I like to coordinate with the top. Pieced ones with extra blocks are pretty cool but usually by the time I get the top pieced I just want to be done!! I Longarm for people and really like busy prints because small inconsistencies in stitches and tension are less noticeable.

My first thought is what thread I am going to use. I love the fabric at JAF with the colored background (such as black, red an pink) with random dots.

I piece all my backs, have done for at least 20+ years.
I like using my stash
I like that both sides end up beautiful, although many have been simple, on the simple side the quilting shows up to advantage when I have that side up.
My backs seldom have anything in common with the fronts :) I mean I don't try to coordinate anything

sometimes when I have a complicated quilt on the working wall, I'll piece a back from a stack of 10-12" block that I've cut to size over the year cleaning up scraps.

I've also used two tops...Bonnie Hunter mysteries for instance. Absolutely love them.
Half the storage space when not on the bed, and 1/2 the cost of having two quilts long armed...

In the end though, the only important thing is you are happy. Right?