Strongest Zoan? I would think it might be a bear or something.
Could be the Schibukai, the guy who's name is like a bear. Can't remember his name that drags along a bible. He could be the strongest animal zoan user i reckon.Just a prediction.
Barthelomew Kuma (Bart Bear). http://en.wikipedia.org/wiki/Shichibukai
Hohohoho!