Shonn Green was the single most talented runner I or any Iowa fan has ever seen in an Iowa uniform. Unfortunately for Shonn he was not here long enough to develop a more complete game. The NFL has no patience for learning curve and doesn't spend alot of time on development. This is why Green did not have a more successful pro career.
Now aside from pure running skill we can talk about best "hawk" RB. This will include length of career and all around skill set. My list is: Harmon, Wadley, Betts and then Green.
Wheger, Adam Robinson and Marcus Coker all had a chance to make that list. They all had talent and potential, but alas AIRBAG made it's hay day against these casualties.