There are myriad of transportation options from the Suvarnabhumi Bangkok Airport (BKK) to the city center. As I travel around the Asia extensively, I often decide to have either along transfer (less than 24 hours) or stop over for a few days in Bangkok. I probably do this 10 to 15 times a year.
My personal choice is the public taxi from the departures level. I used to take the taxi at the arrivals level, but there really is no reason to do that. The SkyTrain is nice to do once, but even then I was questioning myself why I just didn’t take a cab. The AOT ladies are annoyingly trying to push their car service that costs about triple, if not more, compared to the public taxi.