I also have trouble trying to decide exactly how to FMQ my quilts. The first year with my Longarm I just did a meandering/stippling stitch all over and was happy. About six months ago I branched out and do the loopy loops. I've tried to watch several youtube videos, then tried to duplicate the flow of the stitch using a sharpie on a piece of paper. When I find something I like, I will try to practice it several times on paper first before getting brave enough to try it on the longarm. All of the videos on line make it look like such an easy process. I've probably done at least 25 quilts on my longarm, but still consider myself a newbie at it.
While I can appreciate the detail involved in a lot of Leah's filler designs, the thought of spending days and days doing such small detail on a large quilt makes my head spin. If someone ever created an app where you could upload pictures of a quilt and answer some basic questions about your preferences and it could give you several choices for completing the quilting, I would buy that app!