I read that toslink is preferred over S/PDIF, though I agree that unknown variables can tip the balance to either direction.
While Toslink (optical S/PDIF) avoids the potential for ground loop issues and impedance matching issues that may arise with coaxial S/PDIF, it can have issues of its own, related to transducer quality and to slow risetimes and falltimes that can contribute to jitter.
My perception has been that more often than not member posts reporting on comparisons between those two interfaces have favored the coaxial (electrical) alternative.
Best of luck, however you decide to proceed! Regards,