Which Miami Dolphins running back should you hitch your wagon to?

Lamar Miller is the incumbent starter but the Dolphins invested a fifth-round pick in Boise State running back Jay Ajayi this year. Had it not been for a nagging knee injury, Ajayi would have been off the board much earlier and possibly even snuck into the first two rounds. He's a multi-purpose back with a lot of shiftiness and good size at 6-feet and 221 pounds. He rushed for 1,823 yards with 28 touchdowns in 2014. Not a bad resume builder right there.

"He's kind of underrated; had 50 receptions as well," Dolphins general manager Mike Tannenbaum said of the young ball-carrier. "Hopefully he has the ability to be a three-down player."

A three-down player wouldn't leave much room for any other running backs so it's possible that Miami projects Ajayi to take on a lead role.

"Jay Ajayi is the front-runner to back up Lamar Miller and could eventually challenge Miller for a starting job," Barry Jackson of the Miami Herald wrote. But that is easier said than done.

Miller has increased his production every year since being drafted in the fourth-round back in 2012. Last season he set career highs in carries (216), rushing yards (1,099), yards-per-carry (5.1), rushing touchdowns (8), receptions (38), receiving yards (275) and receiving touchdowns (1). That type of improvement will make it tough to unseat him early on but fantasy owners should still  monitor the duo's workload in the pre-season to get a sense of which back the Dolphins like more.