I would do Humphries and two unprotected firsts for Millsap.
Why? The Nets unprotected 1st are only going to give you picks in the 20's. Plus with Millsap they will be significantly better, so that pick may be more like 25.
I'm not taking back Humphries ****ty contract for Millsap for anything the Nets have to offer. They would have to dump Humphries to some other team, but who they **** wants to take that? The only scenario I see would be if someone was dumping a longer-term, slightly less ****ty contract on another team. The Jazz won't take back any ****ty contracts (as so far that has been the only concrete statement on their trade stance). Billy King would have to work some magic in getting a lot of teams to agree on something in order for Millsap to become a Net.