where to stay in Xian when early am flight?

I am arriving in the morning on the soft sleeper train from beijing then staying overnight for 2 nights and departing early in the morning (8 am) the third day from the international airport. I would like to book a 2 day tour of the city to include the terracotta warriors. Is is best to book a hotel in the city or at the airport.? How long before my flight departs should I be at the airport for an international flight leaving China