This series had many, many characters and all got their fair share of development.
For me it's really hard to choose a fav. All of them are wonderful and rounded. Mong is the genesis, but not the story. Ter is such a nice guy. Melon is quite a complex personality. Nich is so dam picky!
The most unliked would have to be the underwear thief because none of the main nor supporting characters are to be unliked!
I really think Ter may be my favourite character! Like you said it's difficult to pick one but episode 20 became a sort of milestone in my mind lol he's such a nice person and he's always kind to everyone. At first glance I thought he looked like a coldhearted person who only cared about living in his own luxury world full of vintage objects, but then he showed kindness, solidarity, empathy, trust in the value of friendship. I really really like him.
I also really like Hall now. I loved his character development. He matured throughout the episodes and became more responsible about his own actions.
The most unliked character...honestly speaking Melon's behaviour kind of irritates me. Some things she did are exactly what I can't stand the most even in real life.
And I can't stand White's mom lol she's rather annoying.
Ter is a "hipster" as he calls it, but really is a nice person. He showed great respect to the Monks and Temple, but he has his style. Jod is somewhat of an opportunist, but he has proved himself to be a good person quite a few times. Hall started out as maybe the character to dislike, but, as you say, he has grown. His dad did a good job with him, although he is a bit spoil. Q. I just feel pity. Having a crush like that, doing all that and your crush never notices :( Melon is just a dramatist, but she has her good points too. Ramida was a good choice, as she is not extremely over the top in her portrayal, which could easily happen. (Eg. Cut as Chomping in U-Prince: The Absolute Economist) White and her brother I know what they are going through. My parents were not like that, but many friends have that sort of experience. White's mom is just an overbearing parent, forcing her children to lie and hide things from her. Ti. Dude's got his goals. Shoot for the stars dude! Although you are not always the winner, I'm sure your Dad is proud of you! Jin. What can I say about Jin? I like him. Hard working and love lorn. I hope he gets the girl :) Nitch: come on girl! Decide! You obviously like Jin! P is a secondary character, but wow. Such a leader/ manager! Thinking of P maybe the most disliked is his wife? Mong is a good character for Ngern. He is not a bad actor, but not really the most expressive. As Mong he has to be sort of reserved, so he is suited to the part. He did the opening justice. Leaving home and embarking on a long, life-changing journey. He also plays the dignified and humble Mong quite well IMHO. It sold the series for me! (Imagine if he played Kongpob on Sotus though! Singto is, arguably, the most expressive Thai actor!) But this is a good role for him.
What I love about these characters is they are people we all know. I went to school with all these characters :). In fact they are still my friends :). The rich guy with the car, the fit one, the smart-man, the overly dramatic, the organiser, the love-lust-never-to-get. Maybe not with the BL or the same sex as these characters, but I know them all. I wonder what character I am? :)