Long distances, good flight options
China is large. If you only visit Beijing, Shanghai or Xi'an, the train can be an excellent choice. For more distant destinations such as Hainan, Xinjiang or parts of western China, a domestic flight can save a lot of time.
My own experience has been positive. On a flight from Beijing to Sanya, there was a proper meal and free drinks. The aircraft also felt modern to me.
What I plan for
For domestic flights in China, I treat the passport as the key document and allow a little more time at the airport. Security checks, large terminals and long walks to the gate can take longer than at smaller European airports.
Online check in may work, but with a foreign passport it is not something I would rely on completely. The counter remains the safest option.
The booking, check in and security checks all need to match your passport details.
Chinese airports can be very large. Arriving earlier usually makes the process much more relaxed.
For me, Trip.com is practical for domestic flights in China because flights, hotels, trains and eSIMs can be planned in one place.
When is a domestic flight worth it?
A domestic flight is most useful when the destination is far away or when the high speed train would take too much travel time. For short and medium distances, the train can still be the nicer option. For Hainan or very long distances, flying is often the more logical choice.