When in Pattaya and you need transportation to Bangkok there are a few possibilities.
Taking a private taxi, minivan or bus are the most common ways to travel but there also is the possibility to take the train although it's not advised. The bus is one of the most convenient and cheapest ways to travel.
There are many busses, about 3 an hour, leaving for Bangkok Ekkemai station. But also a few to Bangkok Morchit and southern terminal. The trip to Ekkemai will take about 2 hours for 119 bht. Busses have AC and are comfortable enough for the 2 hour trip.