I haven't used them for quilts, but I've used Walmart Waverly in other projects. I made pillowcases for nephews and nieces last summer when I went to visit. The only place to buy fabric was WM. They've been washed lots and my sister reports they look good. I've made an apron for my mom too and it's been washed often and has held up. I think both of these projects have been laundered more than a quilt would have been and they look fine.
I'm lucky to have lots of places to buy fabric, but if I lived in my sister's town I wouldn't hesitate to buy Waverly. It beats not being able to quilt at all!