Along with a good number of ladyboy enthusiasts, I have found, over the course of nearly twenty years that Thai ladyboys are the best. In terms of looks and love making the Malaysians and Filipinos along with some Indonesians can compete rather strongly. But in terms of their behaviour I think the Thais are streets better.
Take the simple example of gratitude. Over the years, money aside, I've helped many a ladyboy in small and sometimes big ways. In fact I've ended up giving assistance in bigger ways to Malaysians and Filipinos than to Thais but found that the Thais were far more grateful for much less that I gave!
This got me thinking - why is this so? I trawled the internet for an answer and I think this very well written web site had very good and thorough answers. It covered everything from ego orientation, grateful relationship, religion to achievements. Be prepared for a long read but it's well worth the while. This is it - http://www.thaiwebsites.com/thaicharacter.asp