As a Tarheel alum and fan, i can give ya my 2 cents.
1) Barnes is so overrated. He cannot dribble. turns it over repeatedly when he puts it to the floor. He is a fantastic, pull up shooter, with good size, but that's about it. Honestly as a Heel fan he is the only person outside of JR Reid I wanted to leave early.
2) Henson is the steal. Yes, he is skinny and not as skilled offensively, but he has made massive strides on his offensive game. Last season he would of never pulled up and shot a 15 footer, now he makes them consistently. He has a 7'6" wingspan and is still growing. He is as good defensively as Anthony Davis, maybe better bc Davis has not improved much on D, while Henson has made huge jumps year to year. He has a little bit of an attitude, but in a good way. If you try to show him up, he is gonna come back at you hard next time.
3) Why Marshall is coming out is beyond me. First the injury. I had the same injury in college and I missed the 2nd half of my junior season. There is no way he will play at draft camps or personal workouts. SO his stock will depend on people's opinion on what he did as the PG for UNC. Not a real positive draft position. I seriously doubt if he will be drafted within the first 20 picks and expect him to drop to the bottom of the 1st round or early 2nd round. He is a suspect shooter and takes way too long to get his shot off. NBA guards will eat him up on D as well. Think about who he will have to play - Rondo, Westbrook, CP3, D Rose. No way Marshall can stay with any of them. He is the passing version of Jimmer Ferdette. Skilled but really cannot guard people at his position.
So, Yes on Henson, maybe on the Black Falcon and a big no effing way on Marshall, especially since you will not be able to judge his skills bc of the injury.
I would draft Tyler Zeller over all 3. Zeller is a proven worker, has made huge strides year to year and is a very nice kid.