Potomac, College Park, and Hyde are part of the DC-3 and you can't get in there without being intercepted unless you've been fingerprinted, background checked, and given the secret handshape (which is doable, but you have to do it HERE and IN ADVANCE).
Dulles isn't too bad, if not pricey if you want the most convenience. Lots of ground transportation operations.
Leesburg as mentioned is just further up the toll road. It is inside the SFRA so you need to take that course. Leesburg however does have a little special cut out that lets you in and out VFR without talking to ATC. Manansas requires full participation in the SFRA, and has commuter rail (though you'll have to check the schedule) into DC They also have rental cars.
Gaithersburg (also in the SFRA) is a cab ride from to the metro.
Good info on the SFRA is here.