Best Piece of German Chocolate Cake
Heidelberg Bakery at Lee Highway and Culpepper Street (just west of Glebe Road) does a pretty good German Chocolate. Nearby Pastries by Randolph at Lee Hightway and Lorcom Lane is another good bet.
I doubt that there's anyone here who has tasted every German Chocolate cake in the area, so it's hard to say which is the best. But you can get started on the project based on the recommendations here.