I one hand it primarily - right elbow on the armrest, right hand on the wheel - not gripping the rim so much as resting on the face of the wheel when I'm going straight. It's hard to explain, but it seems like my car's wheel was designed for that posture. I one hand most turns, again, right handed. For slow tight maneuvering, I do the whole butt of hand on the rim, turning the whole thing through several revolutions thing.
In a fast turn or serious maneuvering, it's two hands. Usually just to hold on, as my seats offer no lateral support and I'd be riding shotgun if I made a left turn and wasn't careful.