I know the steel is stronger, but aren't most sand ladders made from aluminum? Are steel units more reliable?
I have both steel and aluminum panels, and I've gotta believe that the steel ones would measure out to be considerably stronger. For example, I'd use my steel ones for bridging, but not the aluminum ones. One the other hand, the steel ones aren't any fun to work with, and you wouldn't want to store them overhead, like on a roof rack, but that seems perfectly sensible for aluminum panels.