i think kei is more intelligent cuz :
1. in last episode kei finished his exam in 1 minute....(and thats supernatural)
2. he runs family bizz while in school
well to ryuu fans no offense....

but ryuu is also smart:
1.solves 1000 questions in like 10 minutes on the other hand kei finished maybe more than 1000 questions in 1 minute...
2. well can get higher place than 7 in SA as said by kei..
3. also helps 2 run family bizz...
Well their both smart.... But kei is more smarter no kei is supernatural!!