Martens is good, but it's hard to get an appointment on short notice. Last time I tried, they wanted me to come in 10 days later to make an emergency repair on a broken (and open) window regulator.
Congressional is even worse, and they don't have a good mechanic.
College Park will see you the very next day, but studying TDIs is a theory course for these guys. When I had a window repaired there, it requires a second trip to make them put the door panel back on properly.
For non-dealer repairs, there's a good hole in the wall place in college park south of the campus. There's another place in Wheaton, but when I had my oil changes there, the guy didn't put on the engine cover properly (not a good sign), but he had impressive VW wall plaques.
In all, I've been very unimpressed with local VW service...