It's a Hainan Airlines group company and as such I've been hearing that there may be some issues with their punitive culture against QAR exceedances. Make sure you look into that. JotaJota on Pprune seems to be very knowledgeable about the Hainan group airlines.
The terms of the contract that just came out from Wasinc seem to be reasonable. I'd personally choose the Guangzhou base over Xian for a number of reasons. One, Guangzhou has more international flights to get out of town on days off. Two, there are many more expats in Guangzhou than in Xian so you'll have people to hang out with when culture shock hits. Three, Guangzhou has a better year round climate ( you really need to spend some winter days in an interior Chinese city to understand what I mean. Home heating, store heating, and restaurant heating just don't exist like you're used to in the western world.). Four, it's close to Hong Kong and Macau so you can make quick decompression/shopping trips.
Typhoonpilot