Here is an analysis of the top Heisman competitors:

Colin Klein
69% passing, 2020 passing yards, 12 TDs/3 INTs
748 Rushing yards, 4.9 average, 19 TDs

Marcus Mariota
72% passing, 2164 yards, 28 TDs/5 INTs
516 Rushing Yards, 6.6 Average, 3TDs

Marquise Lee
1447 Receiving yards, 98 receptions, 13 Rec TDs
110 rushing yards, 0 TDs
18 Total All purpose TDs

Kenjon Barner
1360 rushing yards, 6.8 avg., 19 TDs
219 receiving yards 1 TD

Manti Te'o
92 tackles, 46 Solo, 5.5 TFL, 6 INTs (3rd in NCAA)

Johnny Manziel
67% passing, 2780 Receiving Yards, 18TD/6INT
1014 rushing yards, 6.5 avg, 15 TDs.

Comparing the QBs:
Klein 2768 total yards, 31 TDs, 3 INTs
Mariota 2680 total yards, 31 TDs, 5 INTs
JFF 3794 total yards, 33 TD, 6 INT

Klein has 3 less TDs which you can chalk up to a Sr vs a Freshman, JFF has 2 more TDs and over 1000 yards more against much tough defensive competition.

I don't see Barner or Mariota winning because they are neutralizing each other.

Marquise Lee is averaging over 140 yards per game which is damn impressive but USC probably has 1 more loss and he isn't anywhere near as impressive as some of the others.

Te'o is a good player but I don't know why he is even still in the discussion. His 6 INTs are keeping him in the discussion but would you rather have a guy that averages <1 INT per game or a guy that averages 2 TFL and 1 sack per game (of which the SEC has two)

If you are looking at who is the best player and who means the most to their team, giving it to anyone but Johnny is solely a Freshman bias.