MTR is Hong Kong's transportation system incorporating the rail, buses, and airport express system. You can buy a single-fare ride, a one-day pass, or three-day Octopus pass, including a one journey on the airport express.
The Octopus pass or card is a particularly interesting concept, increasing in increments of HK$50 or HK$100. The card can be recharged at stores and can also be used to pay for your shopping with the readers. A microchip is embedded and can be read easily by just holding it up close to the reader- removal from your card holder isn't necessary. They even sell watches with the microchip installed. It makes for a more efficient society moving quickly.
Taking the airport express is one option for an easy no hassle air-conditioned comfort, with service every 12 minutes from around 6am to midnight.
To save money, take a local bus to the nearest MTR station closest to the airport.
The MTR has been evolving and improving itself. The last time I visited Hong Kong, riding the MTR, I didn't enjoy the experience of tightly packed cars or soulless long benches in the cars. The current design makes it more user-friendly in looks, with a friendly system map using led's, indicating station stops and direction. Transfer points light up also on adjacent train lines.