I only watched the top hudl videos for each at the links you posted, but I saw Cooper breaking more tackles. Crowell seems to have really excellent vision and cutting ability. Tends to break outside more often than not. He's better at seeking open grass as it were. The tackles I saw him breaking were arm tackles. To sum it up, he's better at tackle avoidance based on what I saw.
Cooper was run up the middle much more in his highlights so it's a little murky interpreting the differences, but he's able to churn yards and move a pile after contact. He's also more of a North / South RB. Crowell uses every bit of the field to get loose. There also just seemed to be more traffic for Cooper to navigate through in his highlights. Not sure if the types of scheme and play calls had anything to do with that. It may be that Crowell's running style opens the way better due to his shiftiness.
I'd be hard pressed to say which is better given the projection to the next level, but I think Crowell has better vision and composure as of now, and Cooper may need some coaching and film study to grow in that regard. But he is excellent raw material. He also looked good playing both sides of the ball. Focusing on one position should yield better development.