Formal:
* Au contraire: This is the most common and direct translation, and it's suitable for most situations.
* Bien au contraire: This emphasizes the contrast and is slightly more emphatic.
Informal:
* Au contraire! (Exclamatory)
* Mais non! (This literally translates to "But no!", and it's a common way to express disagreement or contradiction in informal settings.)
* Pas du tout! (This translates to "Not at all!" and is another way to express strong disagreement.)
Examples:
* "You think it's going to rain today?" - "Au contraire, it's supposed to be sunny."
* "You didn't like the movie?" - "Bien au contraire, I loved it!"
* "You're not going to the party?" - "Mais non! I wouldn't miss it for the world!"
Choose the phrase that best fits the context and your level of formality.