I go to DC a couple of times a year for a board meeting and, though I get reimbursed, I try to keep the costs as low as possible. This time I wasn't able to get a decent fare into and out of National, so I'm going through BWI. (I tried Dulles once and that sucked.) What's the best, fastest, and most convenient way to get to downtown DC (near the White House) from BWI? I'm guessing the MARC train to Union Station and then the Metro. How's that trip? Any help from locals much appreciated. Thanks!