Smithsonian means different things to different people. For example the National Zoo, at 3001 Connecticut, NW, and the Renwick, 17th & Penn, NW, are part of the Smithsonian. On the other hand the National Gallery of Art, which is on the Mall, is not a part of the Smithsonian. The geographic area covered by the Smithsonian is quite large. You may want to narrow which of the Smithsonian museums you plan to visit. Rather than looking at Smithsonian/non-Smithsonian, the biggies for DC tourists are the National Gallery of Art, the Smithsonian National Air and Space Museum and Smithsonian National Museum of Natural History. There are lots of others, and some of the popular museums are the Spy Museum and the Newseum. You will need advance tickets for these museums at any time. When visiting DC, my current favorites are the Renwick Gallery and the National Portait Gallery. The week leading up to July 4 hosts the Smithsonian Institution Folk Life Festival on the Mall. On July 4, the Metro is so crowded, that it is very difficult to use the subway. If you are leaving the events, avoid the Smithsonian and Metro Center subway stops, and walk to Capitol South or directly back to your hotel. I'm a fan of Dupont because most of the 3* hotels are close to the Metro, and there are lots of activities in the area. A pleasant way to spend a warm summer evening, is visiting Dupont Circle and walking from Dupont to Adams Morgan. Lots to see. Don't forget a few blocks of 17th Street, NW from N to Q for good local restaurants. As part of a DC visit, you will probably want to see Georgetown, however I would avoid lodging there because the closest Metro is Foggy Bottom (Blue Line), because it is a walk from Gtown to the metro, and Foggy bottom is not on the Red Line. I prefer DCA because you can take the Metro directly from the Airport to downtown. IAD is too cumbersome to get from the Airport to downtown, and the rental car facility feels like it is in West Virgina. I think BWI has a Marc train to Union Station, but it will be a hassle. Suggestions. Don't rent a car. Don't bring a car. Don't think about using a car, except a taxi. If you have to have a car, sign up for Zipcar, which can be found all over NW DC. Some suggestions for while you are in DC. Take in a Free Concert at Tiger Hill in the National Zoo. Take a bike ride or Rollerblade on Rock Creek Park on Saturday or Sunday when the Parkway is closed. Take in a free event at the Kennedy Center. Catch a free concert on the West Lawn of the Capitol. For theater, check out Woolly Mammoth and the Studio Theater