In my opinion，it s better to say HI or HEY to your Chinese friends，while it s too formal and official to say ni hao你好.that s why Chinese people seldom say ni hao你好 in daily life

你好 ( ni hao )

depends whom you are talking to -- you can't say "ni hao" to a group of people

The best-known word of greeting is 你好(nǐ hǎo), a both-third tone in which case the first thrid tone should be pronounced as a second one. If you know nothing about pinyin system, it may sounds like "knee how". But you may find it actually not so often used in real life. A real Chinese would speak as below (in different occasions): 嗨！（hài） - Just the transliteration of "Hi!" 早上好！ （zǎo shàng hǎo） - Good morning! 大家好！（dà jiā hǎo） - Hello Everyone! 最近怎么样？（zuì jìn zěn me yàng）- How are you these days? -- A greeting to an old friend. 去哪儿？(qù nǎ er) - Where are you going? -- A Chinese greeting that’s commonly used when you run into someone. and so on.