I (too) am a big pubic transit rider while I am travelling - so I am happy to contribute my two cents worth:
What is your favorite subway system, and why?
I agree that DC has a good subway system - but - what are the key criteria? IMO, airport access and reach are essential. From this perspective, IAD is weak. My personal favourites:
- Lisbon;
- Singapore;
- Kuala Lumpur.
While I agree that PVG has subway access, I found it very difficult to reach my destination in Shanghai, due to connections and short turns.
What are some of the most enormous subway stations that you know of? How do you deal with them.
Obviousy, this is reason to avoid Shanghai's. Also, London. Is there a workaround? IMO, not really.
There is a workaround @ JFK esp if you want to go to The Bronx or Metro North.
What is your favorite airport for subway access to the downtown area it serves?
San Diego
Do you have any general tips to offer on the systems you know best?
I know Toronto & Montreal the best. My tip is to familiarize yourself with the pubic transit buses in both cities as they are the key to cheap transit to the CBD & beyond.
What's your protocol for identifying optimal station exits?
Google Maps is good. I also use the Trip Planner feature.