Those three are the most frequent areas for providers' incalls in the D.C. metropolitan area. Each has its own advantages and disadvantages, but all three have a number of hotels to choose, which is probably why so many providers gravitate toward these areas. Many providers split their tours of the D.C. area up between some combination of these three areas, which I would recommend, as it maximizes your exposure to different hobbyist demographics.
1) Crystal City has an extensive selection of hotels, many of which are conveniently right next door to each other; in some cases, you could walk from one hotel to the other if you need to change hotels. Crystal City is easily accessible via public transportation, and the traffic and parking situation there is probably the least bad of these three areas. It is also probably (IMHO) the most convenient (or least inconvenient) for the widest demographic of local hobbyists. It is not too far into suburban Virginia for the people coming from D.C. proper and Maryland, nor is it too close to D.C. proper for the people coming in from the outer Virginia suburbs. In other words, it is a happy medium. It is also very close to Reagan Airport, which is probably the most convenient of the area's three airports. There are a fair amount of restaurants there (including great a strip club/restaurant combo), but the area is otherwise slow at night.
2) Dupont Circle is most convenient for those who live in D.C. proper or neighboring areas of Maryland. It is easily accessible via public transportation, but driving into D.C. from the Virginia suburbs and parking there can be a challenge. It is (IMHO) the most vibrant and aesthetically pleasing of the three areas and has more restaurants and nightlife. It will be quieter on weeknights but busier on weekends. D.C. proper is often more expensive. This is my preferred location (I used to live there).
3) Tysons Corner is most convenient for hobbyists who live in the outer Virginia suburbs, but traffic and parking there are often a nightmare. It recently became more accessible via public transportation (the extension of the Metro), but the layout of the streets still leaves it often hostile to pedestrians (e.g. no sidewalks). It probably has the widest selection of hotels, but they are spread out over a wide area. It has a lot of office space, giving it a very corporate feel, and is very busy during the week but slow on the weekends. Personally, I find Tysons Corner uncomfortable and depressing and try to avoid it whenever I can