Singapore - KL by bus
#16
FlyerTalk Evangelist
Join Date: Aug 2000
Location: London
Programs: Hilton, IHG - BA, GA, LH, QR, SV, TK
Posts: 17,008
Some others want to travel overnight and avoid a night's hotel cost
Factor in the dead times involved with air transport and there's really not much difference in city-centre to city-centre travel times.
Factor in the city-centre to airport travel costs.
Factor in the cost of baggage.
Finally, consider that you might have considerable difficulty finding super-cheap fares on Air Asia at the time of day you want, or even the day you want, particularly if it's last-minute travel.
I'd say a sensible traveller keeps options open on such a short itinerary. Personally, I love the train when the timing works: but that's just geeky me!