Not really an issue: Use either one. As mentioned above the breakers inside the coach will trip before the breakers on the pedestal. That is a good point, however, about the 30A plug getting a lot more use than the 50A one. Still, though, if the plug fits in pretty snug it is more than likely ok.
Personally we plug in the RV in the 30A plug, and the car in the 50A plug