If you are looking for a personal tour guide in Xi'an then Michael (firstname.lastname@example.org) is your man. We were only in Xi'an for 24 hours and our prime purpose for the visit was the Terracotta Warriors.
I actually messed up the dates and told Michael of our arrival a day too early - despite the massive error on my part Michael was thankfully free the following day and still able to take us around Xi'an. He picked us up straight from the hotel and took us to the Warriors - he was an amazing guide around, took us to each tomb against the rest of flow of the tourists - and was also very insightful around all of the historical facts. He chose a great place for a traditional lunch and it was good way to get to to know Michael a little more and find out about local cultures and the Chinese way of life. After a snooze in his very comfortable car on our way back into the City we went to the City Wall and a very interesting temple (again missing the crowds of other touristy sights). Finally, before dropping us off at the airport Michael took us to another Terracotta site not so touristy as the Terracotta Warriors - and was a fantastic way to end our day in Xi'an.
Michael speaks great English, is extremely knowledgeable and our experience in Xi'an would have been so much less without him. Book Michael if you can - I promise you will have a truly wonderful experience!