In terms of routing, if you prefer non-stop, IAD is better as SFOJFK noted. Coming from CHC, you have two connections to IAD vs. three connections to DCA.
In addition, the FAA in its infinite wisdom has banned standing on any flight to DCA within 30 minutes of landing, or from DCA within 30 minutes of takeoff. Interestingly enough, the no-standing rule does not apply to any nearby airports, such as IAD, BWI, CHO, RIC, etc.