We had a wonderful stay at the Somerset Serviced Apartments in Xi'an. Upon arrival we were upgraded, for free, to a very large apartment/lobby that was much better than the one we had booked.
The apartment was very large, spotlessly clean, very well furnished, comfortable and with all the necessary facilities. Service desk was very attentive and friendly.
The location is also very good, even if Xi'an is a large city. We were some 10-15 mins by taxi from the centre of town - the Drum Tower and Muslim Area, and yet with plenty of very good options to eat around.