Both are "good" pass catchers. Clay is more athletic, faster, more of a matchup issue for opposing defenses. Lane is a better blocker and gets tough yardage and we all love his ability to bowl people over. Lane will benefit from a full offseason of conditioning. Clay will benefit from a more open field thanks to Wallace and Keller.
From what I understand, if Daniel Thomas, Lamar Miller, and Jonas Gray are our running backs, it's highly unlikely that we carry 2 FB's on the game day roster (assuming that we pick up a TE, making Clay a h-back/fb, as Clay and Keller at TE would be a blocking liability).
i KNOW no one wants Madden being thrown into a discussion, but for purposes of experimentation (lol) i've tried both, and have had more success with Clay. He frequently sneaks out of the backfield uncovered. With Clay, the defense would have to account for the FB on every play. An offensive lineup of Wallace Hartline Bess Keller Clay Miller amounts to alot of pressure on the defense...and if Tannehill is given the green light to scramble more, this could make our offense very difficult to stop.