Formal:
* 您好 (Nín hǎo): This is the most formal and polite way to say "I'm fine" and is used for people you don't know well or are of higher status.
* 我很好 (Wǒ hěn hǎo): This literally translates to "I am very good" and is a more formal way of saying "I'm fine."
* 谢谢，您呢？ (Xièxie, nín ne?): This means "Thank you, and you?" and is a polite way to respond while also showing interest in the other person's well-being.
Informal:
* 还好 (Hái hǎo): This means "I'm okay" or "Not bad" and is a common and casual way to respond.
* 挺好的 (Tǐng hǎo de): This means "Pretty good" and is a more positive and informal response than "还好".
* 不错 (Bù cuò): This means "Not bad" or "Pretty good" and is a very casual way to respond.
* 你呢？ (Nǐ ne?): This means "And you?" and is a way to show interest in the other person's well-being.
Other responses:
* 一般 (Yī bān): This means "So-so" or "Average" and is used when you don't feel particularly good or bad.
* 还可以 (Hái kěyǐ): This means "It's alright" or "It could be better" and is used when you're not feeling great.
The best response will depend on the specific situation and your relationship with the person you're speaking to. You can also use a variety of other phrases to respond to "How are you?" in Chinese, such as "忙碌 (Mánglù)" (busy), "学习 (Xuéxí)" (studying), or "工作 (Gōngzuò)" (working).