I mostly buy Bella solids because of the range of colors.
Last year I purchased a couple of Art Gallery solids from an online store. Silky before washing. After washing it softened up. Not sure I would purchase again.
One of my favorite backgrounds in white/cream printed muslins. These are a little more expensive that straight solids, but I love the little bits of print. One of my favorites that I purchased several times was a light honeycomb design.
I tend to mix solids into quilts or use a solid background when I have a really scrappy quilt so the eye has a place to rest!