that are metro accessible. It all depends on your budget, how many appts u have a day, etc. For me incall in DC isn't really appealing bc I don't see more than one person per location, mostly I do outcalls in DC and rarely incalls.  
Usually I stay in VA area where metro is available and free parking for my guest.

DC has so many great hotels to work in. I'd be more than happy to answer you privately or in the providers thread.

As Ms. Turbay mentioned, the DC area Metro (subway) system is very convenient and makes it easy for you to get around and for clients to visit you without needing to drive. The link to the system map is attached below. Tysons Corner is one of the more popular areas and has several Metro stations nearby. You didn't mention how you're planning to arrive in DC but the Metro has stations at both Reagan Airport and the Union Station Amtrak stop.

Understand that "DC" is a rather large area for the hobby. The vast majority of providers work Tyson's Corner in Virginia. Any hotel around the mall area are fine and easy to reach by car. Some are accessible by the metro, but the vast majority of your customers are going to want easy parking. The Westin is popular, but paid parking. So, kind of a turnoff from a customer perspective because of added cost and paper-trail.  

As far as DC, it is a different market. Most providers stay in DuPont circle because of amenities and restaurants for the provider. Capitol Hill is a major pain as far as hotels and parking. They're not going to be as nice, more expensive, and hard to be discreet for many customers because of high traffic of Capitol Hill business (congressional fly-ins, and more likely you're going to run into somebody you know IMHO.

Having been to many hotels in the DC, VA and MD area, there are a few things to consider and research.  Many ladies in the past have stayed near the local airports (Regan in DC, BWI in MD and Dulles in VA). Many hotels offer free shuttle rides to and from the airport. I have been to several nice hotels in the past near Tysons Corner Mall. A hotbed of escort activity that sometimes causes LE scrutiny. Google it. Stay away from any really cheap hotel like Red Roof inn or ones that have doors that open to the parking lot. Avoid hotels that use key cards to operate the elevator (a serious hassle). Having clients search bushes or under flower pots or hotel computer centers for a hidden key card is very annoying. Paying an extra $20 to park in a parking garage is also problematic, but is the cost of driving your own car into the city. Having a hotel near a metro subway is a good idea. But it takes longer to commute sometimes, plus you have to walk in the rain or snow. I remember having an appt in Dupont circle during a serious rain storm and showed up soaking wet. Plus we are now in the Winter Snow season. Which delays everything and everybody. That is all the advice I can think of. Welcome to DC.

I will provide incall from Arlington down to Woodbridge and all the way over to Dulles and even west of that.
Since you're a prospective visitor it might just boil down to trying out different spots to see what you like best.
First stab at the area you can try like downtown DC & Tysons Corner or Dupont Circle & Fairfax or  Arlington (Crystal City is a popular neighborhood there) & Dulles (Herndon for example is one of the cities that's part of the  "Dulles" area) or some other kind of combination with DC proper and a suburb.  
Not to leave out MD but Bethesda, BWI or Columbia might be options to look into also.
I kind of treat all of the more major metros  (NYC, Boston, Chicago etc etc etc) pretty much the same ... spend a little time in the main city but get a taste of the 'burbs too.
Lots of luck!