For piecing I generally use a 75/9 or 11 , Quilting its a 90/14 . The exception is when I use invisable thread for quilting I stay with the 75/9 or 11 . When I quilt on batiks I always do a test and use the smallest needle I can use. They are very tightly woven fabrics and a large needle will leave holes, particularly on batiks backings. If you have to take out any quilting stitches on a batik .. the holes will show and never completely dissappear.