I generally fly into BKK and then take Air Asia down to Hat Yai but when in Singapore I always take Tiger Air and it works well for me. It is a very simple on and off and quick flight. The crew is very professional and the whole process is easy as can be. This is the only route I have taken but over the years it is always quick and easy and the gate at Changi is easy to get to and the whole process from entering the airport in Singapore to being on the ground in Hat Yai is less than 90 minutes. Thumbs up.