Slow Toslink transitions convert system electrical noise (on both ends) to jitter (but Toslink is immune to ambient electrical noise and doesn’t create ground loops).
Fast coax transition produce reflections on characteristic impedance boundaries, that convert to jitter (deform original edge).
I use Toslink with Benchmark DAC3 (good jitter suppression).
There are some many variables - you have to try both in your system and in your room. Same goes for coax cables - the most expensive one, recommended by others can have poor impedance matching in your system, while the cheap one can be perfect. Pay attention to overall sound clarity since jitter converts to added noise.
USB should be the best, since it cannot directly induce jitter (being completely asynchronous), but can inject electrical noise to DAC affecting D/A conversion timing (indirect jitter).
