if you use muslin sheets, with no poly content, you won't get "pilling". and if you toss them in the washer and dryer a couple of time, shrinkage won't be a problem, either. just look at the content, and match the fabric you are using. if your quilt top has poly fabric, then the backing should match. poly content sheets will tend to pill after a while--but you can get "sweater shavers" for cheap at thrift stores, and most fabric stores--and they work!
i agree with the majority--heck--it's your quilt; use whatever you want to! our grandmothers used whatever they had--feed sacks, used clothes, donated fabric--and they kept us warm and fascinated with the lovely things they made from their hearts and hands.