I would do gentle curvy lines that follow the Bargello waves.

I used to do the loop de loop. Then one day I just started to do the meander and was shocked at how easy it was. At the end of that piece I found some sections had larger meanders than others, but in the next quilt I did a larger meander and it turned out beautifully. I just kept changing directions and filling in corners that had no quilting yet.

I am no help with the quilting but wanted you to know I love the top!

You have more options than linear and meandering. If you use your walking foot, you can do a wide curvy line down thru the bargello. This would give some soft lines but not conflict with the color waves. It would be fairly easy to do at home. I would probably use a variegated thread so it would blend in.

I think I would just stitch in the ditch. The pattern is busy enough by itself. I think anything else would distract from the beauty of the quilt as it is.

Love this idea! This is what I would do if you have not done FMQ. This would look great as a wall hanging. Also, FMQ is fun and ez to learn. Make some small quilt sandwiches with left over material and batting and practice! Have fun with it. It was suggested to me, to have a glass of wine first, so you're relaxed a bit. Haha.

very nice not sure about quilting it!

Love your colors! I think that I would use gold colored thread that has a sheen to it and quilt wavy lines , roughly following the diagonal. It would look like a golden river, LOL!

A good design to start with learning free motion is a gentle curve.
 

Simply beautiful! It reminded me of a creek with varying shades of sand and soil and pebbles. I think gentle curving lines going horizontally across would look like the water ripples going over the creek bed. This shape is a beginner free-motion quilting shape...think cursive lower case m but elongated to be almost flat.

You can audition quilting designs by printing out a photo of your quilt top and putting a clear plastic sheet (I use page savers) over the photo. Next take a dry erase pen and audition the designs you have in mind. Practice on a quilt sandwich of the same fabrics, batting, and thread that you will use in your quilt to audition thread color and check tension before you start on you quilt. Most of all, have fun and show us what you decide.

Thank you for all of the great ideas. I am going to try doing gentle curves following the curves in the pattern. Should be challenging for me, especially on the treadle machine.