Formal:
* Fantastique: This is the most common and direct translation of "fantastic." It can be used in both written and spoken French.
* Extraordinaire: This means "extraordinary" and can also be used to express amazement or wonder.
* Magnifique: This means "magnificent" and is a more poetic way to say "fantastic."
Informal:
* Génial: This means "brilliant" or "awesome" and is a very common way to say "fantastic" in casual conversation.
* Super: This means "super" and is a simple and informal way to express approval.
* Top: This means "top" and is used to express something being excellent or "top-notch."
Other options:
* Formidable: This means "formidable" and is a slightly more formal way to say "fantastic."
* Incroyable: This means "incredible" and can be used to express disbelief or amazement.
The best word to use will depend on the specific situation and the tone you want to convey.