All the fighters mentioned are good, but the greatest Muay thai fighters of all time considered by most who know their muay thai (especially in Thailand) is either the current Lumpini Champion "Saenchai sor Kingstar" whom often fights against opponents much bigger than him and still beats them all easily using technical style and traditional muay boran techniques.
And in the past there was Samart Payakaroon who is like the Muhamed Ali of Thailand, he also had a good international boxing record (most consider him to be the greatest).
And 3rd on my list is Jomhod Kiatdisak. He was a very aggressive fighter who ran things in the 90s, he even gave Rammon Dekker a Muay thai lesson chasing him around the ring for the whole fight. He carried fighting until he was 38, and lost to Pramuk, but I think things would prob be different had the fight been ten years earlier. fight.http://www.youtube.com/watch?v=-_jFwgeL0xE
Over great fighters are Saekson janjira, Anuwat Kaewsamrit and current Lumpini welter weight champ, WBC champ and contender asia winner Yodsaenglai Fairtex