I don't care for Addis Ababa, because of the service. The women who serve there are always very passive-aggressive-rude to me, whereas at Langano they are always fantastically kind. Since I tip well and know how to order and behave, I assume there's some kind of issue with outsiders at Addis Ababa, whereas at Langano they are very hospitable to everyone.
The decor at Langano is cafeteria like and run down, while at Addis Ababa they have traditional seats and tables, but apart from the decor, at Langano they do a lot of traditional things I've come to expect with the food experience, like scorching coffee beans (coffee ceremony), etc.
On the surface, Addis Ababa seems more authentic because of all the trappings. But with their killer hospitality, real traditional things they do, and the food being a little stronger and definitely spicier, I think Langano is (under the surface) the more traditional and authentic place to eat.
I might take tourists to Addis Ababa. If I want someone to experience the signature Ethiopian hospitality, I would take them to Langano.
The owner of Langano recently sold the restaurant to his sister, so I don't know if the culture of the place will change, but the food (which I prefer) should stay the same since they been raised in the same family.
I used to go to Langano, but after a couple of disappointing meals, I tried Addis Ababa, and have gone there exclusively since. I found the food MUCH better at AA than Langano.
YMMV. They also have the coffee ceremony at Addis Ababa.
Addis Ababa Restaurant
8233 Fenton St, Silver Spring, MD 20910