You might have recently received your brand new Google Nexus 6, keenly wishing for a clean experience on the device. Unfortunately, some carriers have decided against it, dashing your hopes and dreams and loading up your new device with bloatware. If you ordered your device through AT&T, it will come clean and stock standard but upon powering it up the Nexus 6 will start a setup process, downloading AT&T's apps onto the device's memory. Luckily, you can get rid of them.
You will need: Nexus 6, one plastic fork, some time and the willingness to root the phone to get rid of the extras AT&T has provided for you to make your Nexus 6 just like all the others. There's an AT&T logo on the back of the phone which can be easily removed with a sharp object, though you could try a plastic fork as well, in order to prevent any damage to the back of your device. In any case, be careful not to scratch the finish off the back of the phone. Also, the logo is quite small and in an embossed black on the black surface, so it might be safer to just leave it there and put a case over the top of everything.
AT&T has made several customizations to the device, including a custom boot animation that plays before the stock animation, a standard set of ringtones that are available on all Android devices AT&T sells, and a SIM lock that prevents other carriers' SIM cards being used in the phone without entering an unlock code. The custom boot animation and ringtones are easily removed by rooting the device. Moving files to a computer is best in case something goes wrong. If you go in via a root file explorer, remount the /oem partitions as a read-write and remove all the files from that partition, they'll disappear on the next reboot. The SIM lock is harder to remove, but you can request an unlock code from AT&T after the device is paid for or out of contract. Otherwise, some third party sites sell unlock codes.
Every United States Nexus 6 XT1103 with an AT&T or Verizon SIM will check the account's subscription status before enabling tethering. The check is hardcoded into AOSP, but it can be disabled if you've rooted the device by adding a line to your /system/build.prop file - "net.tethering.noprovidioning=true" and rebooting. Of course, all of these bloatware issues can be circumvented by going through the initial device setup without a SIM card inserted. Either way, you will have a clean device in the end.