What's the best way to travel from the Regal Airport Hotel to New Mandarin Plaza, 14 Science Museum?

Well, you can take airport express to get to Tsing Yi Station first. Then take Tung Chung Line to Nam Cheong Station and transfer to West Rail Line to Hung Hom Station, Exit D5. After that, walk west around 300 yards to find the destination.
The whole way takes around 50 mins. The ticket fare is 60 HKD per person.