GW has a relatively new business school building with Duques Hall and I liked the facility. I'm not that familiar with Master of Accounting program. At least with the MBA program, GW is not a Top 10 school, but it is also a respected institution in the Washington DC area. It also has a top notch international relations school on site and the campus is nearby the IMF and World Bank.
As a general university, American is not as reputable as GW even though both schools are great schools. As you noted, DC is a government-town, and the flagship, or most notable graduate schools for both of these universities are the law schools. The Washington College of Law (AU) is a Top 40 school or so every year. The GW Law School has produced a number of Supreme Court clerks over the last decade. Both AU and GW ride a lot off their law school's reputations which makes the DC area a top legal market, so regardless which school you end up at, good chance you will get to interact with some law students also interested in your area.
