で一番の

the best in

→ で
phrase Uncommon #14,098
the best in Used before a noun to identify the person or thing ranked highest within a place, group, or category. The pattern is [place/group]で一番の[noun].
JA: この町で一番のレストランに行きましょう。
EN: Let's go to the best restaurant in this town.

彼女はフランスで一番のテニス選手と言われている

She is said to be the best tennis player in France.

生涯で一番の間違いです

This is the biggest mistake of my life.

ジム大学はで一番の景色に恵まれている

Jim’s university enjoys the best view in the city.