Since you have used so many colors of fabric, just about any of them would work well for quilting, however, matching the backing is my preferred color choice. There is nothing wrong with stitching in the ditch. Holds a quilt just wonderfully. Cross hatching would be lovely also - diagonal lines in both directions.
By the way...if you had fun making the quilt and put your love into making it...it is worthy. If someone gets to wrap up in it and feel the love or enjoy the warmth it provides...it is worthy.