1. For me, if thread is balling up it usually means the machine isn't threaded correctly. I just rethread first, and see if that takes care of the problem. If that doesn't fix it, I take the bobbin out and check for lint or fluff or a snip of thread in the works.
2. Unroll some diffent colors of thread onto the surface of the quilt and see how they look. This is going to be down to personal preference. I prefer lighter, more neutral thread, because I am never really trying to call attention to my quilting stitches.