Just saw the other suggestions that got posted while I was researching mine.

For a $30 or so difference, I think I would avoid the stress of driving in an unfamiliar city and dropping off a rent car. For a rental that short you will either have to prove you bought gas or pay a huge top off fee (it was $15 a gallon in FLL last month -- glad I remembered to replace the 4 gallons I used).

I agree that DC traffic is awful. I never drive there.