In order of how I'd expect them to fare:
kid-J! champions > kid geniuses > science fair winners > spelling bee champions
Spelling bee champions don't need to know the meanings of the words, although it's used as an aid in some competitions.
Science fair winners don't necessarily know much beyond, well, science.
Kid geniuses, even the ones with college degrees, have academic knowledge, but not necessarily pop-culture knowledge.
A J! champion, kid or not, generally needs to have a wide base of knowledge.