Admittedly it was a few years back, but based on the experience of acquaintance of mine, and a Hong Kong resident, I would NOT ride an internal airline flight in China, unless it was a life and death issue or close to it. An internal train ride, no problem.
Can I ask why? In May I will be in China and will have the opportunity to ride 2 HSR lines as well as the bullet train to/from the Shanghai airport, but I'm set to fly between Beijing and Shanghai. It seems like its only a 90 minute flight, so I can't imagine it being a disaster.
You're referring to the maglev from Pudong Airport. I rode it out of necessity one night to pick up my sister there b/c Metro Line 2 stopped running to the airport before the maglev closed for the night. For what it is it wasn't worth the 50 Kwai considering you'd probably have to transfer to Metro Line 2 anyway to get to where the majority of the hotels are. Line 2 would cost under 5 Kwai for comparison. Looks flashy from the outside but the interior consists of cheap looking seats with bad seat covers. For what it costs I'd have expected better.
Domestic flights Shanghai to Beijing for the most part leave from Hongqiao Airport Terminal 2 (pretty much the same place as the HSR) and service between the two is very frequent. Metro Lines 2 and 10 service Hongqiao terminal 2. The flight wouldn't be a disaster and you'd even get a meal onboard unlike US domestic flights.