I design liner systems for landfills and have worked with both materials. They each have their pluses and minus. PVC is not UV resistant, so if the liner material will be exposed, this will be a bad choice (pool liners degrade after 10 or 15 years...will likely be worse with the sunlight in thailand). If you are going to cover the liener with soils or rocks....it should be fine. Its advantages are that it is much more flexible than the HDPE, and the fact that you can solvent weld it. HDPE is much more UV resistant (it is usually black from the addition of carbon black which provides the UV resistancy), but it is not very flexible (if you have an uneaven subbase, ir trying to fit around round corners, etc), and can only be heat bonded....typically beyond a DIY installation!
So...if it was me and the liner was being covered, I would use PVC.
Hope this helps!