Mid-Atlantic.
One of the car forums I'm on has a DC/MD/VA section, and it gets decent traffic. Another uses Mid-Atlantic, and it's more active.
Metro DC has as little to do with Atlanta as it does with Montpelier (the Vermont one). Yeah, you get some drawl when you get out in the sticks, but that's true of most of the Appalachians regardless of what state you're in. Both Ex Pres and Sentinel04 are correct in saying that it's neither Suhthrn' nor Nor'eastern.