This might sound odd, but it might make sense to trade BOTH guys. Bradley, Crowder, #16, #23 for Butler and a future 1st? At least in that scenario you're definitely getting the best player in the deal. Regardless of HOW much better he is than Crowder or Bradley, I think most would agree he IS better and will help attract other players.
But think about what it sets up. Chicago gets two players and 2 firsts. Now we unload anything and everything for Cousins. Let's say we offer #3 pick, Smart, KO, BRK picks, MEM pick. Sacramento could end up with the equivalent of 3-5 high lottery picks on top of their own the next few years to rebuild while everyone else chases the insane salary cap.
So now where are we? We've got a "Big 3" of IT, Butler and Cousins for a paltry $40M. Which means we could still sign a max free agent like KD and fill out the roster. For simplicity say we just bring back all "our" guys (Jerebko, Turner, Sully).
IT / Butler / Durant / Sully / Cousins
bench: Jerebko, Turner, Mickey, Rozier, Young, Hunter, some vets
Yeah I know, I turned this into a Durant thing. But the point is- trading both Bradley and Crowder for Butler and keeping the #3 opens some interesting doors.