Theoretically, Kars has 400 IQ, but he acted very irrational.
Dio? Well... he has one of the most powerful power in JoJo - time stop. If he wasn't cocky, he could easily kill Joestar group at the moment when they entered to his mansion.
Kira? Hmmm.... I think he is most consistent villain. He very well used Killer Queen powers (fight with Josuke). Of course, he suffer on typical main villain sickness - he is extremaly cocky, and due this, he said everything about himself to Hayato.
I don't know Diavolo and others, so I don't judge them.
Probably Funny Valentine, he literally commits no mistakes.
But all the villains are brilliant in their own ways though, if not Valentine it'd be a toss up between Dio and Diavolo. They were consistently outsmarting the jojos but had a fair deal of luck though. Their cockiness ultimately didn't affect their battles much.
Only Kira really entered the realm of committing a dumbass mistake that actually cost him victory.