I've watched Mariotta play some and he's good at what he does, but not great, IMO, plus he plays against tiny, unproductive defenses.
Amari is GREAT at what he does. To me, he is clearly the more talented, and certainly plays against bigger, tougher defenses.
But, the talking heads are all in love with Mariotta. He will get the Heisman. That's ok, though. I'll take the Natty over the Heisman any day!