I agree with For The Rebs. Physically and skill-wise, either guy is a good pick. Mentally, Robinson all day. Nkemdiche may end up having the better career if he can figure it out, but Robinson seems to be more of a sure thing.
Looks like he needs to work on that footwork in that video. He's way too high, doesn't sink his hips, and has his weight too far back. It's going to be a rude awakening when he gets to practice in college and can't get by on shear size and strength anymore.