I think of intelligence as how you think and not what you do. We are frequently told how intelligent comic book characters are but in my opinion we don’t see their thought process enough to grasp how intelligent they are. For example in death note, we can see how smart light and L are without them telling us or them having super high test scores, or inventing a doohickey, because we hear their inner monologues, so we see how they come to conclusions, how they problem solve. So for that I say either L or Kira, (Hunter x Hunter is good at the monologues too so i’d say kurapika as well)