Photons have mass equal to their energy equivalent. And relativistic ions have most of their mass in the same form. So propulsion-wise, the two are almost equal

Photons have mass equal to their energy equivalent. And relativistic ions have most of their mass in the same form. So propulsion-wise, the two are almost equal...except that a light emitting diode is much simpler than a particle accelerator. Both would have very poor thrust, of course, and with existing energy sources, the waste mass from the energy production would be disproportional so neither would really be used for anything practical.