Formal:
* こんにちは (konnichiwa): This is the most common and polite way to say "Hi" or "Hello" during the day.
* こんばんは (konbanwa): This is the formal greeting for "Good evening" or "Hello" in the evening.
Informal:
* お元気ですか？ (o genki desu ka?): This literally means "Are you well?" and is a friendly way to greet someone.
* 元気？ (genki?): This is a casual and informal way to say "Hi" to friends or family. It means "Are you well?" in a shortened form.
* やあ (yaa): This is a very casual and friendly greeting, similar to "Hey" in English.
Other options:
* もしもし (moshi moshi): This is used when answering the phone.
* ただいま (tadaima): This means "I'm home" and is used when entering a house.
The best way to say "Hi" in Japanese depends on the situation and your relationship with the person you are greeting.