Which transportation (Taxi or AE/free shuttle) to Royal Plaza Hotel from HK Airport? Family of 4.

Well, you can take AE to Kowloon Station first. The ticket fare is 90 HKD per person. Then take free shuttle bus line K5 to the hotel directly.
Or from the airport, you can take bus no.E21 to get to Mong Kok Police Station, Nathan Road. Then transfer to bus no.12A to Fa Hui Park. After arriving, walk south around 330 yards (300 meters). The whole way takes around 90 mins. It costs 19.1 HKD per person.