Paul McGowan of PS Audio recently posted this on his blog:
He starts off with:
"The Uptone Regen, highly recommended for any DAC"
But then he says:
"I still think Bridge II outperforms even the best I have heard through USB"
"USB is perhaps the worst of any of the formats – optical the best, if only it was glass and not TOSLINK – and Ethernet is probably the least intrusive, if you have a Bridge or something worthy to decode the Ethernet signals"
"On a pure sound basis and without regard for available sources that can do more than stream CD quality, Glass is the best, followed by HDMI, XLR and RCA. USB falls lowest on the list just from this single standpoint because of noise issues"
Why should we listen to Paul?
Well for one he's one of the industry leaders in the high end DAC business. And for 2, since his DAC's have 5 different interface options, why would he have a bias over one or another? Do you really think he would tout an inferior interface as the top recommended for his products?
Yes any company who only has USB as an option, of course, but not PS Audio.