To answer that, you should specify more about your goals for the sump.
If it is nutrient export with minimum care, Chaeto is dependable. I don't like it because nothing eats it and I have seen a tendacy for it to break off and leave parts in display tank.
In general, I recommend Ulva because it is fast growing and everything eats it including people as it is a main ingredient in Nori. The point being, you can exports nutrients or recycle them by feeding Tangs fresh greens.
Patrick