How does one decide what thread to use for quilting?
Well, auditions, of course!
I usually start by gazing at the area to be quilted until I have an idea of how I am going to go about it. Then I gaze at my thread racks and start pulling all the spools that I think might work.
I unwind a bit from each spool into a puddle in the area to be quilted.
Then, I start removing the ones I don't like.
For this "sun" area - I am going with a Superior Rainbows Polyester variegated thread. I like the sheen of this thread, and the color variation is perfect for this area.