With the opening of the KLIA2 budget terminal on 2 May 2014, the simplest and most direct connection between the KLIA main terminal building (MTB) and KLIA2 is the Express Rail Link (ERL). I would recommend that passengers take either the KLIA Express or the KLIA Transit services, both of which are operated by ERL.
The ride takes a mere three minutes and the cost is only RM2 per person. The KLIA2 ERL station is located on Level Two of the Gateway@KLIA2 complex. But please note that you shall have to clear Immigration and Customs first upon arrival at KLIA2 before proceeding to the MTB if you have to catch a connecting flight from there, and vice-versa too.
And if you need to travel to and from the KL Sentral in the city, the KLIA Express and the KLIA Transit services are also the fastest and most convenient modes of transportation available, although the bus shuttles and commercial taxis are also alternatives.
Below is a graphic that explains in a nutshell all the possible connectivity from the KLIA and KLIA2 terminals to Kuala Lumpur and elsewhere within the Klang Valley.
(This graphic originally appeared in The Rakyat Post on 15 May 2014)