I drive a GMC Acadia that has a built-in entertainment system, so my sons can watch DVDs when we're driving on trips of more than an hour. This was a great purchase for them. It also gives me an 110 Volt AC outlet which I can use to charge an iPhone using the standard iPhone adapter. However, the outlet has relatively low power output, so charging takes a pretty long time.
The workaround for this was to purchase a car charger that works with the 12V DC outlet, which has the potential to work faster.
The Incase High Speed Dual Car Charger is one of those USB chargers that does a fantastic job. It charges two iPhone 5s smartphones faster than the standard iPhone charger does when connected to my SUV's AC outlet.
This particular model is somewhat more expensive because it includes one Lightning to USB cable. This is handy if you are using this charger to charge an iPhone 5 or 6-series phone, or a relatively recent model iPad. I keep this Lightning cable connected to the charger at all times, and bring a second Lightning cable in from the house if my wife is riding in the car with me.
I've recommended the Incase Dual Car Charger to friends because it does such a good job at rapidly charging one or two iPhones. Some people look at Amazon.com's vast selection of 12V USB chargers and choose a less expensive model. Please note that some of the 12V USB chargers sold are not sufficiently shielded for Radio Frequency (RF) interference. As a result, they can create a hum that's audible on your car's stereo.