In need of opinions!

Ok, so you know how I said I have my two zig zag quilt tops done? Well, I can't decide on what to do for the backs. The tops are identical, and the binding will be identical as well. But what about the backs? Do I go get enough fabric for solid backs (and if I do, should it be a solid or a print?), or do I piece them with scraps? Do I keep them identical or do I make them different so Spencer and I know which one is "ours"? Help!!

And I apologize I don't have a picture to help with the visualization; the tops are black, white, and red with both solids and prints. Help!!