I've made up my mind I will be getting. Motorola Moto G (2nd Gen) For at&t (US GCM) I also noticed different firmware versions.
Motorola Moto G (2nd Gen) XT1063, XT1064, XT1068, XT1069
Whats the difference?
From Wikipedia:
XT1063 Global GSM, Single SIM
XT1064 US/Canada GSM, Single SIM
XT1068 Global GSM, Dual-SIM
XT1069 GSM+DTV, Dual-SIM, Brazil model supporting DTV
AFAIK any of them should work with AT&T, since they used the 850 and 1900 bands for 3G, which all models have. What the non-US models lack is the 1700 band, which T-Mobile uses for 3G.
In your case it is the XT 1064