I live in MD and roughly equidistant from all 3 airports (as the bird/plane flies). However, traffic can change the amount of time to get to/from each significantly. I will only fly from IAD if it is nonstop and doesn't put me on the beltway at 7-10am or 2-7pm. Metro isn't practical to take red line all the way in and silver all the way out, but I would take it to DCA if leaving from work. Like OP, I am not going out to IAD to go to BOS, esp if it means trying to get home at 4:30pm. Have done AA/DCA or B6/BWI. If am going to ORD or connecting to anywhere, DCA makes a lot of sense and has great connections esp thru ORD, though sometimes prices are higher. I like BWI because it is an easy drive, short security line, close parking, etc., but there is no club and anecdotally I find CPU to be harder(!). Unlike DCA, BWI has an LAX flight, but a lot less ORD frequency and you'll get few SDC options.