My favorite is Mountain Mist Blue Ribbon 100% cotton, but I am unusual in this choice. It is a *very* traditional batting and replicates the look and feel of a vintage quilt. Things I like about it: (1) light in weight with a very soft drape, so is easy to wrap yourself up in the quilt, (2) thin, so I can machine quilt closely with a fine thread and still have a soft quilt, (3) gets softer with every machine wash and dry. I had the opportunity to handle a baby quilt I had made perhaps 20 years ago. It had held up to many trips through the washing machine and dryer and, when touched to the cheek, felt soft as a cloud.
It is getting harder to find this batting, so I am thinking of trying out Quilter's Dream cotton to see how it compares. (Quilter's Dream is needlepunched, so more stable than Mountain Mist.)