Intimate friend: hi（嗨） or their names Normal friend:你好，早上好，中午好，下午好

In fact we usually say "HI" or "Hello" between the friends. 你好(nǐ hǎo) aways use in the first meet.

其实我们就说“嗨（Hi）”，尤其在朋友之间很常用的（familiar friends）， “你好”的话显得正式，比较适合初次见面。

just say hi with your friends 你好 is very official and formal

你好！