Soldato
Fifa I'm guessing, or something like Final Fantasy.
13 editions? in total Although it is fair to say they are very different as the series progressed.
It really depends on how you define iteration.
Generally an iteration is the next level of an existing design.
Therefore FF and Mario do not count as each game is different in both design and implementation. they all play differently, have different engines, mostly built from scratch etc..
Fifa on the other hand is basically the same game just updated every year both graphically and new functionality added. But essentially its the same game.
SF2 is another example.
Therefore I say FIFA is the out ant out winner.