I use 2.75" with about 3/8" seam allowance unless the design or batting calls for a narrower width. That size works well with my walking foot and the batting fills the binding nicely. With each quilt I sew about 10" with that seam allowance and then test that the binding turns over, fills the batting, and ends up right at the stitching on the back. Then, if necessary, I adjust the seam allowance accordingly.