For the highest point of something:
* Sommet: This is the most common and general term for peak, especially when referring to the highest point of a mountain.
* Cime: Similar to "sommet," but can also refer to the top of a tree or a wave.
For a peak in performance, popularity, etc.:
* Pic: This translates to "peak" in the sense of a maximum point or high point.
* Apogée: This is more formal and refers to the highest point of something's development or success.
Example sentences:
* Le sommet du Mont Blanc est le plus haut sommet d'Europe. (The peak of Mont Blanc is the highest peak in Europe.)
* La popularité du groupe a atteint son pic au début des années 2000. (The band's popularity peaked in the early 2000s.)
* L'apogée de sa carrière est arrivée quand il a remporté l'Oscar. (The peak of his career came when he won the Oscar.)
The best translation will depend on the specific context of your sentence.