As of right now, Benson is a must start, especially against Houston. Moreno and Mendenhall are also both very good choices. Personally I would be starting Mendenhall. Cleveland is just too juicy a matchup to pass up.
I would also consider Benson a must start almost every week. He has been an animal and should continue against a weak Texans rush defense. Like the other guy said, the second back in my opinion would be either Moreno or Mendenhall. I would side with Moreno only because Parker might be back this week and I'm sure he will be getting some of those carries