There is no one-size-fits-all answer to this question, as the best controller sensitivity for Fortnite depends on individual preferences and playstyles. However, several professional Fortnite players have shared their own sensitivity settings that might be worth trying out.
Here are a few professional Fortnite players and their sensitivity settings:
-Aydan: 10% horizontal and 10% vertical
-Exhibit: 6% horizontal and 6% vertical
-Hackney: 5% horizontal and 4% vertical
-Kjhovey: 5% horizontal and 4% vertical
You can find more professional player sensitivity settings here: https://www.prosettings.net/fortnite-pro-settings-sensitivity-list/