Etienne will go higher as he is a better receiver coming out of the backfield and that is what NFL teams want. I do believe however, that Johnson will have a longer career because he is more durable because of his size.
NFL really values pass pro for RBs as well. Maybe some teams think they can teach Etienne how to block and get the best of both worlds but my feeling is good luck with that. Etienne is not a willing blocker and a liability on the field. It will be interesting to see who goes first.
Etienne probably presents less risk because few would challenge picking him above Montrell. I'd bet that way but I think Johnson will be a better pro.
It didn't say much for Georgia's offensive depth that Etienne immediately became a starter. A Florida backup becomes the UGA RB1? That's not very elite.