FRM v CAIA

Short of a CFA, which is most useful from a regulatory perspective: FRM or CAIA

What do you mean by “from a regulatory perspective”? Do you work for the SEC? Or are you in some field, like risk management, that needs to deal with regulatory authorities? But anyway, broadly speaking, FRM probably has better recognition than the CAIA. However, the benefits of either are debatable if you already have the CFA.