Unless you are talking about a slab that is going to carry a heavy structural load such as a warehouse or something similar Fiber is the better option... . why? Because in the real world the wire ends up on the ground and is never lifted up or worse up at the top and you cut it when you cut your CJ into the slab... thus leaving nothing holding it together. Nor will the fiber separate when you cut the CJ's. Personal experience demoing slabs that had fiber in them speaking here. In the ideal world wire would be best, in the real world fiber for low load slabs/houses is ideal. My garage slab is 36 by 24 with metal keyway at 12 foot centers in both directions ... ... ... ... 10 years and not one crack. And yeah I park my one ton, Cummins and all, on it every night :-laf