Update (1st February 2016): Price increased to HK$350. (SG$66.36)
Whenever visiting Hong Kong, will always travel by MTR. After all, even our government is looking up to them for their service quality and standards. It is also very comfortable and convenient. So I make a booking online for Airport Express Travel Pass – 2 Airport Express Rides for HK$300. (SG$56.88)
What this provides is 2 rides on Airport Express (Excluding travel between Airport and AsiaWorld-Expo stations.), 3 days of unlimited rides on MTR (Except additional travel on Airport Express, East Rail Line First Class, and travel to/from Lo Wu or Lok Ma Chau stations.), Light Rail and MTR Bus. (Northwest New Territories.)
It is quite economical as return ticket on Airport Express can cost up to HK$180. (SG$34.13) At end of your stay in Hong Kong, you can refund ticket for HK$50. (SG$9.48) So that works out to HK$250. (SG$47.40) HK$70 (SG$13.27) for 3 days of unlimited rides is good.
They also run complimentary shuttle bus service to many hotels. (Including Dorsett Mongkok that I am staying at.) Check out here.
You may book online at here.