It all depends on where your ultimate destination is. I recommended the Tung Chung MTR line (orange one) because it runs parallel to the airport express. It stops at Tsing Yi, Kowloon station, Hong Kong station plus a few others in the middle and all for a price thats far less than the airport express.
Yes buses may be the better solution for some destinations, say for example Ma On Shan which is the other corner of Hong Kong and requires three changes on the MTR network alone. While the bus A41P takes you right there
from the bus terminal at the airport.