As a true running back I think that Derrick Henry is definitively the best RB in the league and in my own opinion it's not even close.
Power, strength, breakaway speed, quickness, vision, durability, in-game endurance... He can make quick jump-cuts and jukes, and has the best stiff arm in the league. Has success out of the wildcat formation, and is a monster on screen passes (not sure why TEN hasn't run more of these yet this year).
As far as I'm concerned the only real knock on his game is that he isn't really great at running routes or catching the ball.