Joker is a shit choice because he's a villain that only succeeds because of the stupidity of others. He's not really good at anything other than being crazy and even then he's outdone by plenty of other characters.
As for my pick...
Griffith because he's such the perfect white knight even after making his deal with the devil. The deadliest thing about Griffith isn't even his own power, but his ability to inspire others to follow him. That and as an antagonist, he brings out the best
most interesting qualities of the protagonist.