I have different thoughts on this one than some other folks - Since the pieced patchwork blocks are SO colorful (and pretty) I would probably go for more contrast in the Sue blocks to make them stand out a bit more and kind of balance the two blocks - i.e. in the block with pink dress and green hat, I would use green thread on the pink dress and pink thread on the green hat, maybe a shade or two darker/brighter than the fabric colors. A narrow fairly short zigzag stitch is nice and quicker than buttonhole but one I made a grandneice several years ago with buttonhole has held up quite well thru numerous washings!