Formal:
* Mon ami(e) extraordinaire (masculine/feminine) - This is the most literal translation and is quite formal.
* Mon/Ma formidable ami(e) (masculine/feminine) - "Formidable" conveys a similar meaning to "amazing" but is slightly more formal than "extraordinaire".
Informal:
* Mon/Ma super pote (masculine/feminine) - This is a more casual and friendly way to say "my amazing friend". "Pote" is a slang word for "friend".
* Mon/Ma meilleure amie/mon meilleur ami (feminine/masculine) - "Best friend" is a great way to convey "amazing friend" in a casual setting.
Other options:
* Mon/Ma super ami(e) (masculine/feminine) - This is a casual and playful way to say "my amazing friend".
* Mon/Ma ami(e) génial(e) (masculine/feminine) - "Génial" is a popular way to say "awesome" or "amazing".
Ultimately, the best way to say "My amazing friend" in French depends on the specific situation and your relationship with the person you are speaking to.