I have decided I like variegated threads best on solid or nearly solid backgrounds. If there are too many color changes going on in the piecing, all the color changes in the thread just seem distracting.
I recently tried quilting again with a Connecting Threads variegated I had previously been very disappointed with. This time I did an all over pebble pattern in Fall colors on a deep brown tone-on-tone and it turned out really pretty. I have also discovered some of the decorative stitches on my DSM look really nice with the CT variegated.