I think we need to keep Daniel Thomas in case Miller gets injured. He simply isnt as bad a player as some on FH make him out to be.
Besides, the other guys seem like specialists so far. I like what I have seen from Gray, but Id like to see what he can do with the 1st units out there. He could certainly be a nice short yardage back. Hell, I wouldnt count him out as a regular back. I think top speed can be a bit overrated. If he can get tough yards and make the chunk gains of 7 and 8 yards when it opens up that is fine. Id like to keep him.
Gillislee at a minimum is a great blocker out of the backfield. He is a must keep for 3rd down passing situations when we want some security back there. He could also develop into a nice all around back.
Id keep Miller as the primary guy. Keep Gillislee as the blocking back. Gray for short yardage and perhaps even a 4th qtr HAMMER. But, I would also keep Thomas as security in case Miller gets injured. If we dont have Thomas Im not certain the other two guys could fill the role of featured back just yet. Thomas could do it. He wouldnt be the best in the world, but he has proven he can play in the NFL.