loose footed mains
The advantage of a loose-footed main is a greater ability to give the sail extra draft when sailing off the wind. The disadvantage is that it doesn't direct laminar flow all the way to the foot in light air, so there will be a bit of spilling as compared to a sail with a shelf. The bottom line is probably this: if you're the type of guy who likes to set his outhaul once at the beginning of a sail and then leave it alone, don't get a loose-footed main. If you're a sail tweaker who adjusts for shape every time the wind changes, go loose-footed. I'm a tweaker myself, and I wouldn't have anything other than a loose-footed main.