It depends on what one's definition of "MVP" is. Mine is "The best player" in the league, period. Any other definition or qualifier statement after that is just garbage in my opinion. In that case it should go to Payton. Sadly, due to the nature of the position, and the way the NFL is now, it rightfully should probably never go to anything other than a QB (and definitely not a running back) for a long time baring something really incredible almost beyond belief from somebody from another position.
I wish the NFL would adopt an award that the CFL gives out in their "Most Outstanding Player" award and split the MVP award into two awards between that and what it is now. That way it could go to somebody that had a special season relative to other players of their type, but not technically be the one who contributes the most to points or wins because of the nature the quarterback position has.
I have to say even then I probably wouldn't even give that hypothetical award to Peterson this year. I would put both J.J. Watt and Calvin Johnson above him in that respect.