That is a tough one.
Lets see the 2 we already saw. Collins was actually a better RB than Faulk (Much better), there was NO ONE better than him at the time.
Now, LF coming in with a lot of hype therefore I would like to see him run his first season.
Now, as the questions stands today and I have to pick one, I will roll the dice with LF due to what I have seen of him at RB, his pass catching ability, and his size. He is a MAN compared to the other 2 guys and I think he will be every bit as good as both Cecil and Kevin. If thats true and he is the "Next coming of Adrian Peterson" then that would be the ideal pick