Re: Moto x on att
There is no reason at all to buy the AT&T version of the Moto X whatsoever. It is both sim locked and bootloader is not able to be unlocked (it might not be needed, but if Moto X no longer get updates in the future, not being able to unlock the bootloader to manually update the phone can be a bummer), lacks 1700MHz support for T-Mobile 3G, and have AT&T logo.
The Unlocked/T-Mobile version support all the bands required to work on AT&T (LTE band 2/4/17). It is pentaband 3G like Nexus phones so it'll get 3G anywhere around the world. Its sim unlocked and bootloader is unlockable. It lacks AT&T bloatwares, probably will get updates faster than AT&T version. So it's a no brainer.