You know what, people are going to say Joker, but Riddler was a heck of a genius with his invention and discovering the real identity of the Batman. Although, most likely he wouldn't have been where he was without the backing of Two-face.
If its short amount of prep involved, I would say Joker. With long prep, Riddler has a chance imo. Joker can't lure Riddler out like he did to Batman, he couldn't care less if he killed people in Gotham.
Arent they the same character? The only difference between the Joker and the Riddler is that one likes to ask a lot of difficult questions and the other likes to wear make-up. This is how we're to perceive The riddler from, Jim Carreys' performance and Bruckhiemers direction. Yeah, the Joker wins because he doesn't care about anything and he's definitely got more ingenuity and patience.
__________________ "If you tell the truth, you never have to remember anything" -Twain
(sig by Scythe)