It's not completely clear cut. Marsh has an elite NFL type arm. He just does. I mean he has an absolute cannon. Coaches get enamored with that. Also March, if you look strictly at his stats, did not do terrible. 7 TD's vs. 2 Int's is good in anyone's book. Then you have the factor that Marsh put in 3 years to the program, so naturally if it's close you're going to go with him over a freshman that just showed up, unless that freshman is clearly way better.
Brown is better than Marsh, but remember we have still only seen a small sample size of Brown. Then you have the factor that Brown was limited to 4 games without burning a redshirt.