你好 or 您好. “你”mean "you","您“ also mean”you“.But "您"is more honorific.

It depends the person you are talking to: 1、您好， usually use to show the respect to him/her, such as person elder than you , person with high social status . 2、你好 is more casul which use between friends or peple with same/equal social status. 3、But sometimes “您好” will show more distance between person are talking than "你好“。

嗨！

你好

depends on whom you are talking to