[Nexus 6 Accessories] jt3:
I thought I'd jump in here and explain why there's so many inconsistent stories regarding cables. Here's the real deal:

Android determines whether a charger is a computer (USB) or a wall charger (AC) by the status of the data pins in the USB connector. In USB, there are 4 pins. The center two pins are data pins. The outer pins supply power and ground. If the central pins are shorted together electrically, then Android devices consider that a wall charger, and will attempt to charge at a higher amperage. If they're not, then the device assumes it's tied to a computer, and charges at 500mA (the power put out by a computer's USB 2.0 port). This is why some 2A chargers will show as "Charging (USB)" on the battery screen, instead of "Charging (AC)," which is what you want. ( I said attempt before, because connecting a cable where the data pins are shorted to a computer won't increase the 500mA that your computer is supplying. Thus, the device will TRY to charge faster, but won't, because it's limited by the computer.)

iOS uses a different method for determining AC/USB, so any charger designed for iOS devices will charge your Android device at 500mA, regardless of the rated power. (That's why some multi-port USB chargers, with a 1A and 2A port will often charge better with the 1A port -- the 2A port tends to be designed for iPads.) Along these lines, there are two types of "Charge Only" cables: Those where the central pins are shorted (Android-compatible), and those where the central pins are missing or disconnected (electrically, that's called "open," which is the opposite of "shorted" -- and these are iOS-Compatible). Thus, using a "Charge Only" cable, can actually be a bad thing. In fact, most "charge only" cables are of the "open" type. So, to say that you should get a "charge only" cable is wrong, more often than not.

Unfortunately, when you're purchasing cables or chargers, they almost never say "Android Compatible." Instead, look at what it DOES say. If it says it's iOS compatible, or that it's designed to charge any iOS device, then it definitely won't charge your Android device at more than 500mA. Stay away! Look for it to say it's designed to charge a specific Android device, like a Samsung S5, or a Droid Maxx, or whatever. Compatibility with ANY Android device, means compatibility with ALL Android devices. (Assuming it's still a micro-USB connector.)

Cables sold by themselves are almost always Data cables. Cables sold with chargers are almost always "charge only" cables, and you need to go by the charger compatibility to determine the cable compatibility. The real test is to find a charger/cable combination that will show up as "Charging (AC)" on the battery screen. The original OEM pair that came with the device is best for this. Once you have that pair of known Android-Compatible components, you can swap out the cable OR charger (ONLY ONE AT A TIME!), and test it to see if it still reads "Charging (AC)," or "Charging (USB)." If it's the latter, then that charger or cable was designed for iOS devices, and won't really be useful with your Android device. If it's the former, then it becomes a known compatible item for further testing.

In summary. The power rating of a charger means absolutely nothing. A 2A charger for iOS will charge much slower than an a 1A charger designed for Android. Don't rely on that. Instead, rely on the device that the charger was designed for. If it says it's designed to charge an Android device (any Android device), then select that over any charger that even so much as mentions an iOS device. Better yet, look for chargers that support the Qualcomm Quick Charge 2.0 standard. That's the same as Moto's "Turbo Charger," and since that's an Android thing, it's guaranteed to be Android compatible, and much faster at charging your N6.