Hi Lilian

Depends on whom you're talking to I guess. I use 'Hi' a lot when I talk to my friends but never when I've a meeting with my boss for example. 

Regards

Karen 

I usually say hello. It is friendly and neither formal nor informal.

 "Hi" is an informal greeting, but it is OK with friends or people you know - we wouldn't use it in a formal situation though. Definitely don't say "hi" at a job interview!

"Good morning" and "good afternoon" are more formal greetings, but its fine to use those with friends too.

Hello is formal and Hi is informal.

Hi is commonly used on emails and the internet.

Hello is nicer and better to use on a first meeting.

Hi can be used after you have gotten to know a particular person or circle of friends, if they use it you can also.

I prefer Hello and use it more than 90% of the time.