It depends on what time of year it's to be used. In the fall and winter the flannel or fleece. I keep a quilt as a spread on our bed in summer using a bamboo/silk batting and cool cotton backing. Also like a lap quilt for laying down during the day to keep the air off legs and feet.

I use flannel as a quilt back regularly but I use a heavy duty diaper weight flannel for backing. It is called Killington flannel and is the best flannel backing fabric. It does not pill and stands up to the wear and tear of a utility quilt. My children and grandchildren love their quilts with a flannel back.