I have used the Quilter's Showcase for backing and it's holding up well. I recently did an elephant wallhanging with one and it was a nice weight and sewed up well. I think the only difference was the colors weren't quite as vibrant as most LQS fabrics, but it wasn't bad or I wouldn't used it. I think the Keepsake line is diminishing in quality. I used a red for a backing recently that was way too thin after washing. I hope it holds up.
I like the new medallion prints in the QS line. I can't see anything wrong with them and the ones I've purchased washed well.
Fabric is such an enigma. Lately my favorite are the Nothcutt Stonehenge and Artisan fabrics and some of their digital prints. They feel silky and a great weight, but they are a coarser thread and fray more than I like. An old favorite, Moda Marble Swirls was thin and silky, but has wonderful colors and washes well. Then I replaced my turquoise and it was not as intense in color and much coarser, but the name and number of the fabric didn't change. What??