I'm working on a quilt that will have a little of both. Will use the embroidery foot with feed dogs lowered for FMQ and the walking foot with out feed dogs lowered for straight line quilting.

From what I've read: when you lower the feed dogs the fabric moves freely for the FMQ. And when you use the walking foot you don't lower the feed dogs so the feed dogs on the machine and walking foot move the fabric through at the same time to eliminate puckering.