AG: I haven't had experience with the Rugged Cover II. Looks like a quality product.
My truck has the Extang Solid Cover, which is fairly popular around the country. Gives you maximum height inside, since it sits on the top of the bed sides as does the Rugged Cover II (no rail necessary). Very strong!
Not trying to point you in any particular direction, the major determinant in these things often is the price point.