Between the two, I would use the aluminum set with the rod ends at both ends. You will get infinite adjustability, it won't need to be disassembled to adjust it, and it will probably be a bit easier to assemble.
You didn't mention who was selling what. I would have thought a double rod end link in steel would be readily available. You could also make you know someone who can weld (presumably you don't weld or you wouldn't ask this in the first place). The threaded ends in right and left handed threads are available at lots of places like Summit Racing and even Amazon. You will have to know the ID of your tube so if you use the tube from original lower links, you'll have to cut one of the ends off one.