I have used warm and white before and the place mats lay flat and the quilting designs show up well.
I made a table runner with white Flannel once, vs the batting. I pre-washed the flannel before using it. The runner stayed flat on the table and I didn't have to worry about how close to quilt the designs. The fabric had a busy pattern and the quilting designs would not show up well anyway. After washing, the runner kept a clean crisp look and not crinkly like cotton batting gives you after washing.