Formal:
* Fabuleux/fabuleuse: This is the most common and literal translation, meaning "fabulous" in the sense of being extraordinary or impressive.
* Magnifique: This translates to "magnificent" and can also convey a sense of grandeur or beauty.
Informal:
* Génial/géniale: This means "brilliant" or "awesome" and is a more casual way to say "fabulous."
* Super/superbe: These both mean "super" or "superb" and are informal ways to express excitement or approval.
* Fantastique: This translates to "fantastic" and is another informal way to say "fabulous."
Depending on the context, you could also use phrases like:
* C'est incroyable! (It's incredible!)
* C'est génial! (It's awesome!)
* J'adore! (I love it!)
Ultimately, the best French word or phrase to use depends on the specific context and the level of formality you want to convey.