There is only one lock for the Steelers at running back. Le'Veon Bell at No.1. Unless some bizarre trade, injury, or suspension occurs, fans know that he has secured that spot. Other than that, all the other RBs are in question. I see the Steelers taking 3 RBs on their roster and their main options (other than Bell) include James Connor, Jaylen Samuels, Stevan Ridley, Fitzgerald Toussaint, and Jarvion Franklin.
James Connor
Connor has still not come back completely from his health issues in college. He still has a lot of potential and is a better receiver than most consider him to be. He showed a lot of explosiveness during his occasional runs last season, and can be a very good power back in the future. He is a lock for the roster.
Jaylen Samuels
The Steelers' 5th round pick has insane versatility and has a very high ceiling. He has played RB, FB, WR, and TE. Samuels is a bigger back with good speed and should make the roster, though spending some time on the practice squad is not completely unlikely.
Steven Ridley
Ridley is a power back and a veteran with experience. His performance against the Browns in Week 17 last year shows he still has some juice and can contribute to the team.
Fitzgerald Toussaint
It feels like Toussaint has been very close to making it to the roster, but he has never really gotten a chance to play. The Steelers signing Terrell Watson over Toussaint and starting Ridley over him as well shows that they don't have much confidence in his play. Yet, he has spent a longer time with the team than both those players, so a return is not impossible.
Jarvion Franklin
Franklin is an absolute bowling ball of a back. He's big and has very good power, especially for a UDFA. But his ceiling is limited and James Connor already fills the role of a power back.
Conclusion: The battle for the No. 2 comes down to James Connor and Jaylen Samuels. I think Connor wins, but Samuels sees more total snaps in total. He'll probably line up at WR occasionally, definitely more than Connor. Samuels is the No. 3 back. Other than the first 3, I would put the RBs in order as: Ridley, Franklin, Toussaint.