You want to stay here!
If you're looking for a clean, comfortable hotel with a wonderful staff, an excellent location, and a great value, look no further. My Dad and I spent the weekend in DC and had a great time, and the quality of the Hilton Garden Inn was a big reason.
Cleanliness - The housekeeping staff really knows what they're doing. I didn't see anything in any part of the hotel that even caused me to raise an eyebrow, never mind complain.
Comfort - I felt at home right away. If you're using a wired internet connection, you'll find jacks on the desk lamp AND both bedside lamps. At the desk you'll find a comfortable, modern, office-type chair. It's easy to miss the fact that your bed has adjustable firmness, and the dial is directly on the mattress, underneath the sheets. I slept like a rock!
Location - You're close to a lot: superior museums, great restaurants, and famous monuments along the Mall. If what you're looking for is more than a few blocks away, take a few minutes to familiarize yourself with Washington's Metro system - there's a station right across the street. Cabs are readily available, too, but it's nice to know you won't have to spend $50 every time you leave the hotel!
Staff - We were impressed. An unpleasant staff can ruin your stay, but that wasn't a problem here. Everyone we talked to was nice, but two really stood out. Raquel, at the front desk, was friendly, helpful, and knowledgeable, and we said hello every time we came through the lobby. Nikko, our server at dinner, was nice to talk to and took very good care of us.
Food - Good. Breakfast was on the better side of average. Yummy and good quality, but nothing surprising. Omelets and waffles are made on the spot. Dinner is better, though. Hotel restaurants generally don't have the best reputation, but this one is worth your attention. If nothing else, have a seat at the bar and order the lamb lollipops appetizer. Yes, I said lamb lollipops. Trust me.