Formal:
* Être intelligent(e) - This is the most literal and formal translation. You can use it for both men and women, just changing the ending to match the gender.
* Être brillant(e) - This means "to be brilliant" and is another formal option.
Informal:
* Être malin(e) - This means "to be cunning" or "to be clever" and is more informal.
* Être futé(e) - This means "to be shrewd" or "to be smart" and is also informal.
* Être intelligent - You can also use the formal "intelligent" in informal contexts. However, it is a bit more formal than "malin" or "futé".
Examples:
* Il est intelligent. (He is intelligent.)
* Elle est brillante. (She is brilliant.)
* Tu es malin. (You are clever.)
* Vous êtes futée. (You are shrewd.)
The best way to choose the right phrase is to consider the context and the person you are talking to.