the price difference between the two boards are not that much, atleast not where i live, so if i was you i would go with the z97, since it has SATA express, and some other features that the other one does not have.
i have the Maximus vii formula myself, and i could not be more happy with it
The maximus vii formula is overpriced IMO. you get pretty much the same features on the hero, unless you have money to burn and planning on a full lcs, the formula isn't really a practical option.