Flying! If your engine dies on the highway you can just pull over. At 10,000 feet, not too many options are available. But then there are certain risks in both, that would be hard to impossible to mitigate. ;)
Actually all scientific studies prove driving far more dangerous. Many many more people die in motor vehicle accidents every year than in air accidents. As in approx 40,000 vehicle accident deaths per year verses 200 plane accident deaths. Based on total miles traveled in both you have a 200 MORE of a chance of dying in a car accident as compared to an airplane accident. Air travel is the safest way to travel.
Scientist proved that driving is more dangerous. It seems that planes are more dangerous but that barely ever crash. It is more common for a car crash to happen than a plane. Just it seems that planes are scarier. But cars are more dangerous.