If you were moving to China for 1-2 years, would you choose Shanghai or Beijing?
Some advantages I've heard for each include:
Beijing:
-"Real" Chinese experience.
-More interesting things to see.
-Has more music & arts.
-More places to go for weekend trips, hiking in nearby mountains, etc.
Shanghai:
-Better weather.
-Less pollution.
-Denser, more manageable city.
-More expat comforts, English speakers, etc.

