Fantasy Upside
Even though rookie Tre Mason is being drafted a full round higher than Cunningham in both standard and PPR formats, it's Cunningham that offers more value heading into the regular season. Things could change in a hurry, especially when considering that Cunningham was an undrafted free agent in 2013 and Mason was the team's third-round pick this past May. But right now it's Cunningham that is coming off the bench when Zac Stacy needs a breather, while Mason has been relegated to third-string duties. Through two weeks of the preseason, Cunningham has done nothing to deserves a demotion as the Rams' No. 2 back. If Stacy were to fall victim to injury early in the season, Cunningham would ostensibly take first-team reps. He's the better handcuff for Stacy at this present time.
Fantasy Downside
We alluded to this in the "Fantasy Upside" section but it bares repeating: Cunningham is currently running with the twos but things could change quickly. The Rams didn't draft Mason with the 75th overall pick so that he could ride the bench for most of the year. He offers more long-term upside than Cunningham and is the more dangerous option in the passing game, even though Cunningham has shown plenty of burst in open space.
Bottom Line
Unless Stacy suffers an injury, Cunningham will remain the No. 2 back until Mason shows enough potential to deserve a promotion. Even though Mason is the more touted back, Cunningham is the better handcuff for Stacy owners heading into the season. Just understand that Mason was drafted to eventually provide the lightning to Stacy's thunder and the coaching staff may want to see more of the rookie as the season wears on. The good news is that the Rams are a run-first team and will likely get all three backs - Stacy, Cunningham and Mason - involved on a weekly basis. The frustrating part for fantasy owners is that the dynamic behind Stacy could change throughout the season depending on who has the hot hand. But Cunningham has some value, especially now that Sam Bradford is out for the season and the team will be forced to lean even heavier on their running game.