1st - General tasks that don't require sending anyone to a job, with Krustyland ones at the end;
2nd - Springfield Heights crafting tasks, ordered the same way as these currencies are unlocked;
3rd - Tasks done by only one character, ordered by the level which the character is unlocked (Homer-->Lisa-->Ned,etc). If there are two tasks with the same character they are ordered by time;
4th - Tasks that require group collections, with no specific order yet.
The point is to be easy to find the challenges, as to me it doesn't make sense putting for example Ads at the beginning of the table then at the end put the Pharmaceuticals, like you suggested.