WE are in Xian for 4 days? Please suggest MUST SEE / NOT TO BE EVER MISSED sites and TOUR options?

The must-sees include Terracotta Warriors, Huaqing Hot Springs, City Wall, Big Wild Goose Pagoda and its squares, Shaanxi History Museum and Qinling Wildlife Park. In addition, there are many other sites worthy visiting like Small Wild Goose Pagoda, Tang Paradise and Muslim Quarter.

As you will have four days, I suggest you join a trip for a better sightseeing. Then I would recommend Travel China Guide to you. It is located in XA and offers the best service. They also can arrange a home visit in the city. If needed, here is their contact for your reference:
traveltravelchinaguide.com