Fastest way from HGK airport to Nathan road in Kowloon? Thanks in advance. Gijs

Airport Express + Taxi is the fastest way. You can take AE to Kowloon Station first. Then take a taxi to Nathan Road.
Or take AE to Tsing Yi Station. Then take Tung Chung Line to Nam Cheong Station and take West Rail Line to East Tsim Sha Tsui Station, Exit N5. Then walk west around 80 yards to arrive at Nathan Road. The whole way takes around 50 mins. It costs 60 HKD per person.
You can choose the way you like.