Tbh there isn't much difference with digital transports, in my experience transports are the 1% of the audio experience. Unless its one of those old cheapo 16-bit USB modules which have a bit of an effect on output(could of also been the dac as well).
One of the advantages of optical is being completely isolated in its own world, with its disadvantage not being very efficient jitter wise
Usb is much like spdif for most people, one of the hidden advantages of USB is you can get part of the advantage of optical by not using the PC ground, and replacing the power lines with a separate power supply. Its plug and play most of the time, you buy it, plug it in and your good to go. Some of the most advanced standalone transports are USB!!!
coaxial is just old school, everything oldschool just works perfectly. I personally prefer it but I also use a dedicated sound card for it... which takes effort. If your on head-fi you are smart enough.
That is my opinion, it is neither right nor wrong just a different point of view.
Edited by ninjikiran - 8/7/12 at 8:03pm