Reminder for the #WHY2025 attendees: There are two main chemicals used in mosquito/insect repellents, #DEET and #icaridin (aka picaridin). Both are about equally effective.
In case you don't have a preference for either, my recommendation is icaridin. That's because DEET is a solvent and can damage plastics, synthetic fabrics, and other things. I've once permanently damaged my tent simply by touching it with DEET on my fingers.
Also, DEET interacts with sunscreen, making it ⅓ less effective.