Tua Saranyu, Sam Yuranan, Willy McIntosh, and Wirayut Rotocha from the 1988 version of JLR are some of the best veteran actors in my book. As for the middle generation, Ken T. and Chakrit are the only ones who have impressed me. Aum is good, but he is only good in aggressive roles. His roles in Dao Kiang Duen and Maya Tawan were mediocre. He's not very convincing when he plays a gentleman or anything else. For the new generation, Weir, Toomtam, Es Kantapong, Rome, Porshe, Great, and Phet are good actors but not as advanced as the veterans that were mentioned. I know some may be reading that list and disagree, but please, with all bias aside, watch them and judge based on acting and not solely on appearance.
As for the veteran actresses, of course Anne is on top and still is on top. Lol. Mam Jintara is another person who is praiseworthy. Also Aom Phiyada. For the middle generation, there is only Noon Woranuch. As for the new generation, Matt Peranee, Sammy Punthita, Now Tisanart, Kwan, and Kimberley are the ones who have the most potential to lead the future ET when it comes to acting skills alone.
I feel like I'm forgetting some.