So if I want to hold is better to keep my Bitcoin in a wallet or in an exchange ?
You should hold your Bitcoin in a wallet, preferably a ledger nano S or trezor for more security. Another difference of holding BTC o exchanges is that the account you use to hold your Bitcoin in an exchange is easier to hack than a wallet who have seeds(private keys) that cannot be easily guessed(although it can be obtained via phishing if you are not careful enough).