Many have Kalil rated higher than Martin, but I give the slight edge to Martin. Both of these prospects could come off the board in the top five.
Offensive line prospects are evaluated based on their ability to play left tackle. Those capable of playing on the left side tend to get selected early in the draft. Both Kalil and Martin project as NFL left tackles. This is a demanding position, as it bears the responsibility of protecting the quarterback against the pass-rush.
The NFL continues to move toward more of a pass-oriented league. This fact only increases the importance of having an elite left tackle on the roster.
Martin does a better job protecting the passer than Kalil. He possesses better foot speed, balance and technique. The biggest edge Martin has over Kalil is his fluid movement.
Martin plays with great balance and change-of-direction ability. This allows him to anchor and react to any counter-moves.
Kalil has a tendency of lunging, which results in his shoulders out in front of his feet and an unbalanced stance. Poor balance allows the pass-rusher to effectively employ counter-moves.
He also doesn't possess elite foot-speed, which is needed to protect the edge against speed-rushers. This issue is exacerbated by some wasted hand motions. He has a tendency of shuffling with this hands at his side, forcing him to wind up before delivering a punch.
Football is a game decided by inches and seconds, meaning even the smallest waste of motion is important.
Both are effective run blockers, but this is where Kalil has an edge. He plays with a lot of aggression and explodes into the defender. This allows him to get a push off the line and open running lanes. Martin also does a good job firing off the ball but doesn't create the same push as Kalil.
These are two prospects who will come off the board very early. The difference between the two is minimal but significant enough to rank Martin over Kalil. I have some concerns about Kalil's future as a left tackle. There might be a point in his career where he needs to be shifted to the right side.