Reed alone has more intellectual creativity and Bruce would be an able assistant. So, for coming up with a scientific plan to save the world or something I give it to them.
BUT, for something well-known in the comic universe, like building a robot, I give it to the Leader. He has an enhanced mind, not just a smart human mind. So he could think faster and add efficiency to the engineering and fabricating process. It's something like having super strength vs being a very strong human. The very strong human could still be a better dancer or fighter, but in a test of heavy lifting s/he would lose. Building a robot is (mental) heavy lifting.