It is a rare occurrence that a running back with Lamar Miller's talent and skill level gets released to free agency however it appears to be happening.
Miller is only 24 years old, and for running backs the age scale gets a bit skewed but this guy is not even in his prime, he is just getting started. In 2015 Miller played and started in every game and has actually only missed 3 games in his entire NFL career. Miller recorded 194 rushing attempts, 872 yards, 8 touchdowns, 397 receiving yards, and 2 receiving touchdowns.
In Miller's career he has had 638 rushing attempts, 2,930 yards, and 19 touchdowns in total. Miller was largely underutilized in Miami so he will still be pretty fresh for an NFL running back.
Miller wants to be utilized as a work horse back and there are only a few teams that would fit that mold. The Tennessee Titans, Dallas Cowboys, New York Giants, Indianapolis Colts, Houston Texans, and New England Patriots will likely draw the most attention do to their holes at the running back position. Miller would fit nicely with Indy but would likely split time with Frank Gore, the same would be the case for New England who have several capable backs.
Really the primary focus would be on Tennessee, Dallas, Houston, and New York. Miller was born in Florida and went to college in Florida so it is safe to say he would probably not like to leave but a change of scenery might help his career a great deal.