Just completed a stay at the Renaissance Hotel in Washington DC. It is not located on Dupont Circle but several blocks away. However the location is very central and convenient to restaurants and many DC sights.
I highly recommend this hotel -- the service is outstanding -- from the front desk to the concierge to the wait staff in the restaurant. The manager has really done a great job training staff to make guests feel welcome.
The design of the hotel is crisp, clean and modern. The lobby,bar area, restaurant,& fitness center are great. I had read that the rooms were on the small size so we were prepared. When we checked in, we must have been upgraded (I didn't request one as it was a short stay) for the room was quite large and well furnished. We arrived on a Friday so I knew the CL would be closed. I half-jokingly asked if they "could do something" about breakfast. With a smile, he handed me chits for buffet breakfasts in the restaurant! That's what I consider a Marriott/Renaissance Reward.
As the hotel is situated right in the heart of the DC hub, parking is expensive ($35+/night). However the great location makes the tradeoff worthwhile. We would definitely stay here again.