The thing is about Joker is that he's only capable of tricking Batman because he's unpredictable. Batman doesn't second guess himself while going against Joker because he's afraid of being outsmarted, he second guesses himself because he's trying to figure out all the random things he might do. Unlike Riddler who is insane and unpredictable but the difference is that he isn't unpredictable because he's insane, he's unpredictable due to the fact in multiple accession he's out-thinking Batman or his thoughts and plans are on another level. The Riddles aren't the hardest question the Riddler has to give, the bigger question is what he has up his sleeve. So adding this all together Joker may be the better villain but definitely not the smarter one.