I play around with designs in Quilt Wizard and recently got EQ7, which I'm still learning what all it will do...and how to get it to do all it's good stuff!
Mostly for actually doing a quilt I just sort of play it by ear and let it happen. Sometimes I really like how it turns out, other times not so much...the main reason I got EQ7 was to be able to put my fabrics in for a 'test drive' to prevent some of my more 'blah' (not enough contrast) outcomes. I have a tendency to have all the fabrics too close to the same "medium" colors.