I've been recently researching this area myself. It's been the subject of fairly passionate debate. There's one school of thought, which is "bits is bits" and neither the cable type (toslink vs. coax) nor brand should make much difference.

The other school of thought is do not use toslink if you can avoid it and get a good coax cable that has a true 75 ohm RCA connector. The reasons? From what I can gather: (1) the connection on toslink is not as good as coax; (2) toslink is more prone to jitter; and (3) coax has a wider bandwith. There's also something about the inherent weakness of toslink converting light as the input signal, but I can't remember the particulars of the argument to do it justice.

Anyway, I haven't done any A/B comparisons of the two. However, I am currently upgrading cables throughout my system and plan to make a length of coax and compare it to the toslink I am currently using on my Oppo DVD player. If your a DIY-type, the digital cable made by DH labs (D-75) with their 75 ohm RCA connectors can be had pretty cheap online. (BTW, I do not work for or have any affiliation with said company.)

I plan to order this combo soon and will report back my results if anyone's interested. Be forewarned, I'm the same guy who heard differences between my stock power cord and an aftermarket brand.