If you are considering DC during the rest of 2016, keep in mind that Metro will be single tracking quite a bit during that time. They are doing a major safety related overhaul and use of the system will be limited significantly for the rest of the year. Late night operations are being curtailed for this period.
Before choosing a hotel read the following: http://www.wmata.com/Images/Mrel/MF_Uploads/SafeTrack_Public.pdf
Choose a hotel close to your destinations and check the maintenance schedules so you can avoid the tie ups. Just to give you an idea, Orange line trips that typically take 30 to 40 minutes are currently taking 60 to 90 minutes.
Good advice phctourist. Actually I think the work is actually over a full year, so it pays to check before traveling there.I escaped the District last week, just before the SafeTrack initiative started. I am going to try to minimize my trips there, but unfortunately there is no way for me to eliminate them. Another good source for information is the Washington Post. There are a number of free ways to get access to the online version, such as registering with a .gov email address or my local paper includes WaPo access. Here is a link to one of their summary articles, SafeTrack closures: These D.C. Metro lines and stations will be disrupted in the next year - Washington Post.
While this work is a pain if you are having to commute, but totally necessary. I had a colleague who was on the train that was in the tunnel with the electrical fire outside the L'Enfant station. Suffered smoke inhalation and was transported to the hospital to be checked out. Fortunately he was ok. A lot of coworkers are just taking taxis due to concerns about safety. I still typically take the Metro when in town but hard to argue with their logic.
Most of the activity seems to be outside the downtown area, but July has some impacts if you are taking the Metro from DCA into town. Any of my stays will be close to downtown where I can walk, take a cab, or use the Metro if not impacted in the area. I have stayed at the JW, the Mayflower, and the Washington Marriott Georgetown. All have pluses and minuses depending on your needs and tastes, but would recommend them all. Haven't stayed at the Metro Center Marriott but colleagues have given it good recommendations.