I would say Harry Potter is by far a better series as there is a lot to be learnt from it. In fact, scientists have proven that children who read Harry Potter are more subject to better concepts. It teaches them to respect stigmatised groups. Do not get me wrong, Percy Jackson has a very good storyline just like Harry Potter but I would say that the writing style is vague and conversational. Harry Potter teaches us to fight for the best things in life and if you examine the series there are a vast array of quotes that will definitely improve or life if followed.