We chose the Residence Inn Pentagon City for our long weekend stay in DC due to price and proximity to National Airport. Pleasantly surprised; we arrived at the hotel and checked in early, expecting to have to leave our bags and come back that evening for our room. Instead, they got us in to our room straightaway - a 2-bedroom suite (as requested) that turned out to be on the 17th (top) floor, with a nice view of the Potomac and the airport. Hotel is a short walk from the Pentagon City metro station, as well as the Fashion Center mall and food court. (NB: Just around the corner from there is Naked Pizza, which actually has gluten-free pizza crust!) Pentagon metro station is also a short walk to the north - both Pentagon and Pentagon City are stops for the blue and yellow lines, either of which is convenient to the National Mall / Smithsonian.
Breakfast each day at the hotel was complementary, but very crowded at the time we ate - around 9 am. Not a huge selection, but what was there was good, especially the biscuits and gravy and the make-your-own waffles. (Coffee, however, did not seem to impress my daughter, who is spoiled by Starbucks.)
Only disappointment with the hotel was upon arrival; we probably waited 30-45 minutes for the hotel shuttle to finally come around. We tried calling the hotel front desk, but the phone would ring many times and then would get a message that "no one was available to take your call. You will now be disconnected. <click>". When we finally arrived at the hotel, there were only two people working check-in, and the phone was ringing off the hook with no one able to take time to answer it. Not the best first impression for newly arrived visitors.
We had no problems with our early shuttle back to the airport, which was right on time. Overall, a great stay: good, convenient location; clean, comfortable rooms; friendly staff (though perhaps stretched a bit thin). Would definitely stay here again.