Is it an unquilted top? And you want to machine quilt it? If so, I would definitely not do stitch in the ditch; it would be a nightmare because of the uneven piecing, and SITD would draw attention to the uneven piecing. I would maybe quilt concentric circles around the pieced circles, fill in the circles with a flower design, and finish the other unquilted areas (open areas left after quilting the concentric circles) with a geometric design. I think this would enhance the design. Monofilament thread would be a good choice for machine quilting. If you are thinking of hand quilting, monofilament would not be a good choice.