I love taking the airport express. It's fast, comfortable and super convenient. When I used to live on HK island, I would always go to Hong Kong station and take the Airport Express to the airport. It takes just 24 minutes, and the train is very spacious and comfortable. I almost never have to sit next to anyone because there are so many seats! If I'm not wrong, there is free wi-fi on the train too, though if you live in HK you probably wouldn't need it as you likely have a 3G plan (as most HKers do).
A train ride from Central all the way to the airport will set you back $100, so it's definitely more expensive than if you were to take the airport bus. But seriously, the Airport Express is so much more comfortable, and faster too. On buses, there are lots of stops along the way so it slows you down, and if you happen to be travelling at a particular busy hour you might not even be able to get a seat on the bus! With the Airport Express, you are pretty much guaranteed a seat (or two).
If you're travelling with friends, I would suggest that you meet up with them at the station to buy group tickets together. They have bundles of up to four tickets sold together, making the cost of each ticket a little less. It's not truckloads cheaper, but it's better than nothing!
What makes the journey so speedy is the fact that they are only three stops between HK station and the airport, but that is a little of a disadvantage too. Since moving to the New Territories, I haven't been able to take advantage of the Airport Express because the New Territories stop - Tsing Yi - is nowhere near Sha Tin, where I live. Oh well, the airport bus does the trick, but I miss the days of being able to take the Airport Express to and from the airport! read more