I have the 12 on the Sony a6000 as well as the 14 on the Fuji...not quite an apple to apples comparison.. To me, the 14 is just as good as the 12.. Since I had the 14 before the 12, I would not go back for a 12. I bought the 12 as a combo w/ the 32 when they had the combo sale for 799 (price went back up by a lot - I think I caught a b&h overstock sale..way below the normal sale price). I have not seen it at that price since for the combo lens deal
The 12 is just a hair sharper, not enough to worry about.. I think it will be more which focal length works best for u.
The only other comment is fw updates, the 12 may need to be sent to the factory (the fw update for the Sony version certainly did). The Fuji version of the 12 is always more expensive than Sony version due to extra cost associated w/ the aperture ring.