Formal:
* น่ารัก (naa rak): This literally means "cute" or "adorable" but is often used to mean "nice" or "pleasant" in a formal context.
* ดี (dee): This simply means "good" and can be used to express that someone is a nice person.
* ใจดี (jai dee): This means "kind-hearted" and is a very positive way to say someone is nice.
Informal:
* น่ารัก (naa rak): This can also be used informally, although it might sound a bit childish.
* ใจดี (jai dee): This can also be used informally.
* นิสัยดี (nit sai dee): This means "good character" and is a more informal way to say someone is nice.
Examples:
* คุณน่ารักมาก (kun naa rak mahk): You are very nice. (formal)
* เขาใจดี (kao jai dee): He is kind-hearted. (informal)
* เธอมีนิสัยดี (tur mee nit sai dee): You have a good character. (informal)
It's important to consider the context and who you are talking to when choosing the right phrase.