Personally I prefer the AT&T (or even better, the S type glass). By comparison the coax and balanced connections sound dirty (but one man's dirt may be another's ambience). Certainly, AT&T enjoys far greater bandwidth than coax and XLR and so should produce a square wave with sharper corners etc. But there is always some danger in such general rules. From experience, it depends on what the maker of your gear has thrown the most money at. If the maker recommends say XLR, then this is probably because she/he has put more effort into the performance of this output/input. And yes there are differences. I once compared the use of a Meridian 500 transport with using the Meridian 508 as a transport. The performance of the 500 was vastly superior, and I asked Meridian why. The answer was simple - since they expected the 500 to be used as a transport (and not the 508) they had put a much better output module on the 500.
