I agree that wide backing fabric is usually the most cost-effective. 108" is 2.5 times as wide as standard quilting fabric, but is rarely 2.5 times more expensive. My second choice is the diagonal seam, but as some else pointed out, that won't work in every quilt. Next choice is horizontal seam(s). Pieced backs can be good; the key is to offset the piecing instead of laying it out in a grid. I do not like vertical seams at all.