Henderson is a very good back but he has trouble with nagging injuries.
He is best as a 2nd back that where he plays 30 - 35% of the time. You don't lose much if anything if he has to start over Akers as long as it is only for a few games.
He blocks really well for smaller player, is really good catching passes out of the backfield and runs inside pretty well for a smaller back. I don't see him getting beat out of the 2nd running back job & excepting the injuries, he and Akers are not very far apart IMO.
Williams though is ready to go as he can pass block and catch the ball coming out of the backfield. He is also a tough runner, just not a home run threat. Running backs get are always getting dinged up so I expect he will see plenty of action this year and be ready to replace Hendo who is in the last year of a contract.
I do think he beats out Funk who will also make the team.