I live about a 6 min walk away from the NoMa station (1 stop north of Union on the Red Line), and it usually takes me:
-35 minutes to get to DCA (transfer at Gallery)
-75 minutes to get to IAD (transfer at Metro Ctr, transfer at Rosslyn to bus 5A)
-65 minutes to get to BWI (connect at Union to MARC, transfer to shuttle bus)
Because of my location, I should prefer DCA and BWI over IAD. But for some reason, I absolutely hate going to BWI. I find the amenities at the airport (specifically the AA concourse) to be outdated and the concourse to be dark and old. Mentally I think it is further simply because I have to take commuter rail to get there when I can take Metro/Metrobus to DCA and IAD. Yes, I know Metro also has a bus to BWI, but Greenbelt is far for me and the bus schedule isn't convenient. I hate the shuttle bus from the BWI rail station to the terminal as well. It's always crowded.
I actually prefer IAD over DCA. I really, really like Concourses A/B. They are actually two of my favorite terminal buildings in the US. I also like the Priority Pass lounges at IAD. It's always fun to see the foreign flagged carriers at IAD, as well. There is usually no one ever on the 5A bus, and it is pretty quick.
DCA is good, as with TSA Pre and Clear, I can show up just as my flight is boarding and simply walk on. It's crowded though, and I don't think the amenities are as nice as IAD.
RJ85, F70, E135, E140, E145, E70, E75, E90, CR2, CR7, CR9, 717, 732, 733, 734, 735, 73G, 738, 739, 744ER, 752, 753, 762, 772, 77E, 77W, 789, 319, 320, 321, 332, 333, 343, 359, 388