On 23rd August 2010 two new railway lines were inaugurated in Bangkok. The City Line is a commuter line that also links through to Suvarnabhumi International Airport. The Express Line is a dedicated airport link.
Both lines operate only between 6am and midnight, a major potential downside. Suvarnabhumi is a 24 hour airport. With ever longer check-in times, it is particularly difficult making many early morning departures using the new rail links.
City Line
The City Line runs trains every 15 minutes. The trains are capable of 160 kilometres per hour, taking approximately 30 minutes from Phaya Thai to Suvarnabhumi. The cost is 45 Baht.
There are six stops between Phaya Thai and the airport. Mostly, these are of no relevance to tourists. The exceptions is, possibly, Ratchaprarop.
Phaya Thai is an excellent interchange with the BTS Skytrain system. That said, expect something of a walk, and unaided by luggage trolleys.
BTS Skytrain
Phaya Thai is on the BTS Sukhumvit Line, giving quick access to the stations between Siam and Phrom Phong, all of which are important to tourists, particularly in terms of their accommodation. To be specific, these are Siam, Chit Lom, Phloen Chit, Nana, Asok (with interchange onto the MRT metro system) and Phrom Phong.
Siam may be used to interchange onto the BTS Silom Line, giving quick access to National Stadium. In this area there is quite a bank of accommodation in the side sois off Rama I. More importantly, you can get down into the Bangrak area for its sights, shopping and accommodation around Silom, Surawong and Charoen Krung Roads. The infamous Patpong is in this area too.
Sala Daeng station is particularly useful as a gateway into this whole district. Sala Daeng also has an interchange onto the MRT metro system. Be aware, particularly if carrying baggage, that this interchange is a fairly long walk.
Express Line
The Express Line operates direct non-stop services between Suvarnabhumi Airport and two city destinations, Makassan and Phaya Thai. Departures are every 30 minutes, at a cost of 150 Baht to either terminal.
Makkasan only has any particular relevance if you are flying Thai International Airways. A remote check-in facility is available at Makkasan, but note that you must check-in at least three hours before departure. Also, remember that the facility is only available from 8am to 9pm.
The journey time from Phaya Thai to Suvarnabhumi is 18 minutes. From Makkasan to Suvarnabhumi takes 15 minutes.