Dear Suzan,
How can I determine the quality of fleece?

Home Sewing Association gives the following guidelines:
1 Density: "Is it dense and thick, or thin enough to show threads under the fuzzy surface? The denser the fleece, the better the quality."
2 Recovery: "How good is the memory: Gently stretch the fleece and let it relax. Does it quickly bounce back to its original dimension or does it wave and ripple? High quality fleece has quick recovery."
3 "Rough It Up": "To give yourself a preview of how will the fabric will wear, rub the fleece roughly against itself, in a circular motion, on both sides of the fleece. If it looks a bit rugged, starts pilling, or distorts, it is a lesser quality fleece. High quality fleeces go through multiple shearing and velouring processes to reduce piling."

Stonemountain and Daughter carries a large and wonderful collection of High Quality Fleeces.