Formal:
* 女孩 (nǚ hái): This is the most common and neutral way to say "girl."
* 女性 (nǚ xìng): This is more formal and literally means "female."
Informal:
* 姑娘 (gū niang): This is a more common and informal way to say "girl" and is often used when talking to a young woman.
* 小姑娘 (xiǎo gū niang): This is even more informal and literally means "little girl."
Other options:
* 女孩子 (nǚ háizi): This is a more informal way to say "girl" and literally means "female child."
* 女生 (nǚ shēng): This refers to a female student.
Which one to use?
* Use 女孩 or 女性 when you want to be formal.
* Use 姑娘 when you want to be informal and friendly.
* Use 小姑娘 when you're talking to a young girl.
The choice ultimately depends on the situation and your relationship with the person you are talking to.