I like Sulky Blendables; it is 30 wt, and I find it a bit more forgiving (very nice, since I'm still getting the hang of free motion!) The colors change about every 2 1/2 - 5 inches. I use So Fine in the bobbin, and adjust my tension to 1.6 on my Designer 1.
Here's a pic of the throw I'm currently working on with it. I've put it on hold for the moment, since DH is promising to get my table finished today. Otherwise, I'm fighting a 3 1/2" drop between the machine bed and the table top (double yuck!)