Deciding what lines to quilt is always a challenge. Quilting lines change the design in ways that are hard to foresee. I wish I had before and after photos of all my quilts to study.
In this case I started off “stitching in the ditch,” which means following the seams of the patchwork with my quilting lines. My thinking was that part of what was interesting about this design was that the areas of solid color were actually made of many small pieces, so I would emphasize that. Some of those lines I liked, and some I took out. By then I was in the rhythm and decided I was also interested in extending and joining some of the lines where seams on one side of the quilt lined up with seams on the other side (for example, the diagonal connections that cross the vertical grey band, in the detail shot), so I did that. Eventually, it felt done.