most of the flannels from joannes & other (big-box) stores will pill with one gentle wash---try a good quality double sided (quilt shop) flannel- I love the Benartex flannels & the woolies from moda are really nice too- wash gently on a short cycle- you just want to remove the sizing, & then Pre-shrink in the dryer-
single sided flannels pill much sooner than double sided (meaty) flannels.