Agree with comments above about IAD--you can take Silver Line Express bus to connect with metro or 5A.
Silver Line Express runs every 15 (?) minutes whereas 5A runs hourly I think. So it would depend on where you're headed and what the timing is when you arrive. I personally take whichever comes first. 5A is quite fast because it only stops once or twice between IAD and Rosslyn Station.

Chicago CTA is also good though two caveats: (1) at one point I arrived and the machines would only take exact change in cash. But presumably now they take credit cards. (2) At some times I have found the train to be a bit desolate and uncomfortable when traveling as a solo female. YMMV.

Transit within both cities is quite good.