If you have an iPhone with MagSafe, you should really get a MagSafe car mount. This includes magnets that hold the phone and then you don't even need to plug it in each time.

I've tried the ESR haloLock mainly because if was only $35 and it works well. The magnets are strong enough and it uses a micro-USB, you just need to find an 18W charger for the 12V as that is not included. The one that Apple sells is the larger Belkin Car Vent Mount which is$40 from Amazon so very reasonable if a bit larger. And it doesn't include charging which I really needed.