natural light is def best.
For the commercials and real magazine shoots they will light the entire car with multiple lights all grouped together in one big light.
The goal is to cut down on reflection. Indirect or dispersed light is best. Aim for a cloudy day.
The pros who shoot cars in studios with unnatural light (which is like everything you see on TV and in print) will go so far as to have some PA spread Vaseline over every curve and corner to cut down on reflection.
here is a good example for you.
this car was shot with a multitude of lights at a variety of angles:
this one is a studio enviornment shot with multiple lights grouped together behind a diffuser, lit from directly above the car (you can see how the light tends to "block" out areas as opposed to the first car where you can pick out multiple reflections.
