The cord makes a HUGE difference. Keep in mind that there are going to be two main types of USB cables. Power/Data and Power only. Most all USB cords are going to be Power/Data. I have a small collection that range in charging output from 0.5amps to 1amps. I have two of
these one straight and one coiled. I recommend straight (you can get a 3 foot black one for $5.50 if 6 feet is too long). Anyway, they can charge a device at 2.1amps (provided the device will accept that much, of course). Potentially higher than that as well I suppose.
Your cable is a big deal. The stock cable is fine, but it's not as fast as the Mediabridge. No cable that does Power/Data is going to charge as fast as a dedicated Power cable due to half your pins being dedicated to data transfer instead of power. Some people have had bad results with the Mediabridge cables. Both of mine are almost a year old. The straight is fine and the coiled has started giving me issues. But I have used it extensively in the car and done a lot of tugging on it. For $7, I recommend buying a couple straight cables. I travel with mine and if I need a data cable, I have a random cable or two sitting in my backpack all the time. For the car, I pair the above mentioned cable with one of these
Belkin chargers that will output at 2.1 amps. I can charge my Moto X from essentially dead to full in around an hour depending on usage while it's charging, of course.
Like I said, your cable is a big deal.