We really enjoyed staying at the Hilton Garden Inn during our recent trip to DC. It was on the blue line which was convenient from getting to and from the airport and all the sites. It's walking distance from most of the museums and government buildings. Everyone was very nice and they were able to accommodate our early check-in.
The only thing they could do better is restaurant recommendations. I like to ask local people for recommendations because they live there and know the places the best. When asking for a dinner recommendation, the front desk staff offered me a list nearby places which isn't helpful in knowing what is a good place to check out