Not wanting to sound "quilt-policey" but the whole idea about IN THE DITCH is that you use a straight stitch in the seam so the stitch itself disappears. Anything else is an SID quilting variation and I personally like them a lot. My last rug mug got a lovely serpentine stitch. (Before then, I would use straight stitch with a few glasses of wine and I ended up with a serpentine stitch lol.) I also like top-stitching on the high side. It's your quilt. Do what makes you happy.