Mutianyu or Badaling

Both sections are good to visit in March, for there is no public holiday during that time and visitors won't be too many. For reference, I personally prefer Badaling. The public transportation is very convenient to either section. To go to Badaling, you can choose to take train S2, bus no.877 or bus no.919. If you decide to visit Mutianyu, it is recommended to set out the tour after Mar. 15th, for there would bus no.867 taking you directly to the scenic area, which would save a lot of your time.
Have fun!