The best option from those provided would be CoderDojo.
CoderDojo is an international network of free coding clubs for young people. It focuses specifically on helping youth learn programming and other technical skills in a supportive and collaborative environment, making it a great fit for your goal of encouraging younger people through programming challenges.
FBLA (Future Business Leaders of America) focuses more on business leadership and skills rather than programming. Hack Club is also a good option, but CoderDojo’s specific focus on coding and its community aspects may be more aligned with your goals of engaging younger learners in programming challenges. CS First is a Google initiative that provides coding activities, but it is more of a curriculum than a club structure.
Thus, CoderDojo is the most suitable choice for creating an engaging and supportive coding community.