It depends on what the OP means by "a better bet."

If looking for sleep or more food options to occupy the time at the airport, I'd go with ORD (someone above mentioned the O'Hare Hilton, a very nice hotel that's attached to the terminal). If looking for an opportunity to see the city, I'd definitely go with DCA and take the metro into the city to see some museums & monuments. The train is easy to find, cheap, and takes less then 10 minutes to get right into the heart of the city. Getting back in through security is easier at DCA as well.