A complete study of the magneto-optical (MO) and magnetoplasmonic properties of both epitaxial and polycrystalline Au/Fe/Au multilayers as a function of Fe thickness is reported. An increase for both the MO activity without surface-plasmon-polariton (SPP) excitation and the magnetic modulation of the SPP wave vector for epitaxial structures compared to the polycrystalline ones is observed. This difference is related with the larger interface roughness of the polycrystalline structures that as a consequence, exhibit a reduction in the Fe MO constants. A comparative study of the MO activity with SPP excitation for both epitaxial and polycrystalline structures is also presented, being the key factor in the deposition of the adequate layer thickness to achieve optimum SPP excitation with independence of their crystalline nature.