I can give you some feedback about CA, I fly with 2-3 times a year (mostly EU-AU/NZ).
- Seats are fully flat - vary by aircraft type (Boeing fleet - same as sCO on B787's, Airbus fleet - same as TK or LO, new A350's same as AC)
- Food is surprisingly good (I normally have Chinese dinner and Western breakfast)
- Service is consistently good, F/A's are nice and polite - always
- International flights are mostly on time, domestic are late (not CA issue - Chinese military 'owns' 80% of air space, very little left for civil aviation)
- IFE improved a lot, but still a bit mediocre
- PEK Lounge is average and crowded, PVG is better (and based on your UA departure airport you might be able to use UA Polaris lounge on your outbound)
- Transit in PEK is bad - long, slow moving lines
Certainly not a bad alternative, IMHO better than UA.
Fly Air China, that is a much better improved airline.