I agree that Mathews is the easy keeper. I'd have to rank the rest of them CJ, Graham, AJ. There just aren't enough RBs that have the opportunity to touch the ball as much as CJ does.
Mathews is the lock. As far as the other guys is there a cost associated with each, or just that keepers take the top 2 rounds. If there isn't a cost then I would lean towards CJ. RBs are really thin this year, and CJ was great at the end of the year, I think he will be back to a top 5 candidate this year. Getting 2 top RBs will be much more important than a top TE. However if Graham is gonna cost you something like a 9th round pick and CJ and AJ are like a 3 and 4th, then I go with Graham before I can finish typing this and hit "submit"