Heading to DC this weekend.

I've got a super cheap car reserved. Staying at BWI and planning on 1. Not renting car and taking MARC each way both days into/out of DC. or 2. Using rent car to go to Greenbelt Metro and starting there.

Anyone want to chime in on what might be best? I do like having a car to go to dinner in Baltimore, but that's not a deal-breaker for me.

Also, if anyone has a better suggestion on which Metro station might be better, I'm all ears.