MSNBC:

For decades, the standard instruction was that drivers should hold the steering wheel at the 10 and 2 positions, as envisioned on a clock. This, it turns out, is no longer the case. In fact, driving that way could cost you your arms or hands in particularly gruesome ways if your airbag deploys.

Instead AAA, the National Highway Traffic Safety Administration and many driving instructors now say you should grip the wheel at 9 and 3 o'clock. A few go even further, suggesting 8 and 4 to avoid the airbag mechanism as much as possible, but what formal research has been published on the varieties of hand positions suggests that this may lessen your control of the car.
...
That means the higher up the wheel your hands are, the more likely they are to be directly over the plastic cover when it opens — that is, when superhot nitrogen gas flashes and inflates the bag at 150 to 250 mph.

Among the injuries the NHTSA reports from improper placement of the hands when an airbag deploys are amputations of fingers or entire hands, traumatic fractures and a particularly stomach-churning injury called "degloving," which — trust us — you definitely don't want to look up.

But my car has those little bumps on the steering wheel at 10 & 2 that make holding there so much more comfortable!