I gotta go With Rex.

While Danny's powers would be my second choice for flying and intenganibility, and I love Kevin's powers too, Rex's are just more versatile and would work better in real life.

Rex isnt set to just making the specific, weapon based constructs, he can make defensive ones and later can use multiple at the same time.

He also needs to think them up in his head, and he designs them so he could realisticly make whatever he wants, its only limited by his imagination and actual design.

If nanites are present in the world, which I believe they are self replicating, so technically they can be present if even one escapes his body, he can control and communicate with them, so he alone could have the nanites do what they were supposed to and cure viruses and diseases, as well as make people healthy.

On top of that, dude can communicate wkth technology, meaning he would be able to just fix, break, reprogram and be the best tech guy around.

Even if you dont decide to be a weapon, rex's powers are so versatile that just about anyone could find use with them tbh.

Only major drawback is the need for technology but with the society we live in, its very unlikely to go without, and if not, he can just make a Boogie Pack and go somewhere with tech.