Could you be a bit more specific as to the purposes of your trip? Whether it's business or leisure makes a difference because of location.

I would hands down recommend the Ritz-Carlton Georgetown as the best hotel in DC, and one of the better city hotels in the United States. It has a boutique feel--endless passages, intimate service, and only 80 or so rooms, but all the amenities of a five-star property. If you're in DC for pleasure, it's right in Georgetown, so dining options are plentiful. You do, however, need a car or the patience to walk to the metro in order to see the full city properly. The suites at the hotel range from 900-1200 square feet, and are only marginally more expensive than a standard room. In particular, the corner suites overlooking Wisconsin Avenue are fun places to be.

If you're in for business, it's a bit tougher. I've heard wonderful things regarding the service at the Jefferson, but the rooms are not large, views minimal, and the location isn't even that great. You may want to check out the Hay-Adams for larger rooms and the best location in the city (well, if the White House is your thing). St. Regis, Ritz DC, and Park Hyatt are all also solid, if not great, choices.

I'm not a fan of the Four Seasons or Mandarin Oriental. The latter is too removed from the action and the former is a bit snobby for my tastes, especially considering the rates they command relative to the other properties listed here.