Weekly challenges should be split into categories that people can choose which catagory to receive. Here are is an example that would probably work well to satisfy most people:
Beginner: Easy challenges, meant to get new players to try different classes, weapons, and play styles. Low XP yield.
Silly: Challenges like melee kills, road kills, kills inside of 25m with snipers, etc. Widely varying xp yield depending on difficulty.
Support: Things like supply X ammo, revive Y players, heal Z hp, repair W vehicle hp, get V transport xp. Moderate xp yield.
Squad: Challenges like capturing points with your squadmates, following squad orders, reviving squadmates, healing squadmates, resupplying squadmates, getting assists/kills with squadmates, etc. Moderate xp yield.
Hardcore: Challenges meant to challenge skilled players. High xp yield.
Mixed: A random mix of all of these. Very widely varying xp yield.
Tl;dr: Add categories for different styles of play to weekly challenges that people can choose.