For me it was close between Smart and Brown. Brown because I'd like to see what he grows into, I think the kid is gonna be a starter shortly. He'll make his mistakes this year, and become a strong asset.
But I chose Marcus Smart, not because he's going to be a "star" or even an all-star. Just because of what he brings to the attitude of the team when he enters the game. Marcus is a warrior, he plays very hard, when he defends he assaults opposing players with his aggressive D. Like the night he swarmed all over Cousins, to the point Cousins threw him to the ground out of frustration.
He has enough size, length, and toughness to cover 1 thru 3, and some 4's. As he becomes a veteran, he'll score enough to someday be on a club that seriously contends for a championship.
As we can see, we're missing him in this short stint where he's out. I'd hate to loose his gritty attitude.