As much as I absolutely hate straight line quilting (I don't hate the look I just hate doing it LOL) I think option 2 would look the best, or stitch in the ditch with black thread, then you won't have as many thread changes.
A swirly design would also look good but with a clear thread, but that is always tricky when you are not sure how the quilt will be treated afterwards, a black thread would be too distracting to your gorgeous quilt. Good luck with the auction
