It seems that the properties within the core cities (DC, Arlington, Alexandria) all move in lock step on pricing -- particularly in peak seasons, like cherry blossom or during Congressional sessions. Another drawback to these properties is that parking tends to be very expensive at them.
Are you going on a weekend or a weekday? Weekend parking at Metrorail Park & Ride lots is free, whereas it's impossible on weekdays. On the other hand, commuter rail/bus service to the suburbs is hard to come by on weekends.
Sheraton at King Farm is a good bet; there's also a shuttle headed to the Metro, some convenience shops within walking distance, and if you have a car you can pretty easily get to other things around there like the Washingtonian outdoor mall or downtown Rockville. The Sheraton Washington North in Beltsville is about a mile from Metro, but in a less interesting area.
If you're going just for a weekend, then Metro park & ride becomes an option. National Harbor has two SPG hotels whose rates generally track conventions local to there and not the broader hotel market. It's a about 5 miles from the Metro Green Line (I-495 to Branch Ave or I-295 to Anacostia), which has plenty of parking, or to the Yellow Line in Alexandria, Va. There's also a half-hourly bus (NH1) to the Green Line. SPG has a bunch of hotels further out in Northern Virginia (Tysons, Reston, Dulles area); the Tysons hotels are a few miles from the Dunn Loring station on the Orange Line. Reston, Herndon, etc. are only accessible via toll highway.
If you really want to save money or points, there's a 4P out in Manassas (on I-66, 15 miles west of the Vienna Metro) and there are the BWI/Arundel Mills hotels, with shuttle buses available to the relatively frequent MARC/Amtrak service into Washington Union Station.
Oh, I see you did state your dates and they're weekdays. For then, it looks like Rockville is the best buy.
Last edited by paytonc; Feb 1, 2011 at 11:23 am