XLR vs AT&T st type glass? help

My Transport has 4 different outputs. I want help in chosing the one that will be best. The XLR output is 110-ohm 4V p-p and the AT&T ST glass is -12dBm, 875nm,62.5/125um fibers I don't know what the AT&T means please help me understand is the AT&T going to give me better sound quality or the XLR? please help. My dac has XLR and AT&T Thanks
Both formats can give excellent results, I used both in the past. AT&T is optical, very fast and transparent and the best XLR cables can be a bit less sterile and more involving.
You really have to try, because there is no fast rule.
It will depend on the components and your taste.
If it's a Wadia they recommend the AT$T glass as the highest performance with XLR next. Not sure if other mfg's feel the same...
Try both and go with what sounds best.