The quilt does not care which way you piece the back.It all depends on how big your quilt is. I usually piece the backing vertically because it seems to take less fabric. Most of my quilts are 75x90 so I piece 3 yds vertically which gives me a piece of backing 90 x 108. I usually rip my salvages off and have the fabric cut into 2- 3yd pieces. I pieced a backing fabric once from leftover pieces of fabric and never again. What a pain!!! Also by using one color backing you do have to worry centering it on the toip.