Thanks for the date information. There are a lot of city-wide sellout conventions that take place in DC, so knowing the dates and price range help. From the prices I shopped, it looks like a good time to go.
It really comes down to this: do you want it cheap, convenient, or good quality? Pick two.
Cheap: Look for places that provide free parking, since there is a car involved.A lot of DC hotels charge fees for parking that some people forget to factor in. Hotel taxes vary by location. Downtown DC does, or at least used to, charge addl. taxes for a convention center fund, and taxes in DC, Virginia and Maryland vary. The further out from the downtown market usually means a cheaper rate, unless there is some special event going on in the immediate area.
Convenient: Selecting a hotel in the downtown area will obviously be the most convenient for what you want to do. Most of the museums are within walking distance, so it doesn’t place you at the mercy of a Metro schedule and take up more of your limited time together. There are plenty of hotels close enough to a Metro station that you can walk, or the hotel may offer shuttle service to it. It just adds on to what will probably be a very long day the further out the hotel is.
Good Quality: There are some things that I won’t sacrifice for the sake of location or rate. Cleanliness is one, and product is another. Service is important to me when travelling on leisure and I’m not familiar with the location. And if I had my heart on using a hotel pool, I’d want to find one that wasn’t closed or in poor condition before I booked the reservation.
If it were me, and based upon the information you have provided, I would look into the Hampton Inn options in the Dulles area if you want cheap. Some of them are close to the Metro line and may offer complimentary shuttle service to a station. It will take freaking long to get into the city, but they are typically clean and have quality bedding. Plus their breakfast is much better than economy hotels because they are required to offer a variety.
If you use that reservation search link, I’d add in Homewood Suites and Embassy Suites as options, if you are willing to share a suite. Both offer a more extensive breakfast and a manager’s reception in the evening.
The Embassy Suites in Old Town Alexandria is nice as it is close to the Smithsonian and a very short walk to the Metro station. It’s the one I’d choose if the rest of the party was willing to share a bathroom. They also have a refrigerator and microwave should you want to chill beverages or reheat leftovers. Old Town is a wonderful, historic area should you want to take a stroll once everyone gets back from touring…and lots of great restaurants.
Another thought: you might want to select a location based upon the airport being used if someone is flying in. You mentioned that you had a car, but not the others. Old Town Alexandria is near Regan National Airport and a Dulles location would be much closer to Dulles. Depending upon their flight times, it might make it more convenient and less worry to choose a hotel location closer to the airport.