Hate to say it, but Crowder.
Yes, he's on a great contract, BUT Brown is on his rookie deal and there is a ton more upside in him.
Also, if the C's do sign Hayward, I think he could take Crowder's minutes. He is the better player between the two, and his defense is solid as well (not bad at all).
That being said, I think ultimately you have to decide between Bradley/Crowder OR Bradley/Smart going forward (because Bradley and Smart become FAs in summer of 2018). Brown looks untouchable right now unless it's for someone like Anthony Davis.