Formal:
* 您好 (nǐ hǎo): This is the most common and polite greeting, used for anyone you don't know well or are meeting for the first time.
* 早上好 (zǎoshang hǎo): Good morning.
* 下午好 (xiàwǔ hǎo): Good afternoon.
* 晚上好 (wǎnshang hǎo): Good evening.
Informal:
* 你好 (nǐ hǎo): This is also a common greeting, but a bit less formal than 您好.
* 嗨 (hài): This is a more casual and friendly greeting, similar to "hey".
* 喂 (wèi): This is used to get someone's attention, similar to "hello" on the phone.
Other:
* 你好吗 (nǐ hǎo ma): This means "How are you?"
* 你好，好久不见 (nǐ hǎo, hǎojiǔ bù jiàn): This means "Hello, long time no see."
The best way to say "hi" in Chinese depends on the specific situation and your relationship with the person you are speaking to.