Flight
This is definitely the most convenient airport (it even has its own metro stop!), but you can usually find cheaper flights into Dulles International Airport or BWI (Baltimore/Washington International Thurgood Marshall Airport).
House Or Rental
There are a ton of Airbnb options in DC, which would be especially great for those of you in large(ish) groups. We live in the Hill East neighborhood and would highly recommend something in the area.