How to write it？
▼私、わたし、わたくし、ワタクシ
We usually use kanji and read it “watashi” or “watakushi” depending on the situation.
In casual scenes, we read “watashi”, and in formal or business scenes, we often read “watakushi”.
Children who haven’t learned the kanji yet use hiragana わたし.
わたくし is rare to see.
ワタクシ seems to be used in the cases where a writer wants to express the funny or playful personality of a person who says it.
▼あたし、あたくし、あたい
They are used in casual situations.
あたくし sounds a bit snobby and あたい might make classless impression.
▼僕、ぼく、ボク
We usually use kanji. It is usually used by men. But sometimes women use this word too. In this case, I feel that the female often has a boyish personality and tends to write it in hiragana or katakana.
▼俺、オレ
These are usually used by men. We can see both in kanji and katakana, but rarely in hiragana.
▼儂、わし、ワシ
They sound older. They seem to be used as a dialect in Hiroshima, for example. I don’t think we see them much in kanji.
Advanced Tips
There are several other ways to write “me” in Japanese. Please have a look at the URL below!
Kotoba no Hibiki 