Metroliner DC - Manhattan is the way to go! Especially in First. You get a meal that beats most airline FC meals (and certainly beats the peanuts on the AL or DL shuttles) and you're downtown on both ends. Unless you're that guy who holds up departure by getting to your airplane twoinutes before departure time, it's also a lot faster.
Even if you don't go first, the hot dogs in the snack bar are the best you'll find anywhere.