The guy to grab in this situation is and always has been Antowain Smith IMO. Even if they decide to use Stecker as change of pace (likely), Smith is going to get the majority of the goalline looks and hold the most fantasy value.
Chatman was brought in as insurance in case either Smith or Stecker went down, because neither Smith nor Stecker will be expected, or asked, to carry the workload like Deuce was. I expect him to take a couple weeks, or myabe several weeks, to work himself into a role on the offense.
I think your average game split will look something like:
A.Smith - 18 carries, 1 catch
Stecker - 6 carries, 3 catches
Chatman - 2 carries