I didn't have enough fabric for a whole cloth backing, so, I made the back a theme from the top.

I've done that diagonal method. It really works and it is actually pretty easy to do, BUT you need a lot of floor space (or a big table) to do it. I don't have that much floor space and I was only doing a lap size and it was hard to have it all laid out. But it did work.

I heard that a pieced backing using some of the same fabrics from the quilt makes it appraise at a higher value.