If I may warp the question a bit, the Batman villain I'd most like to see portrayed in a future film is the Riddler. I actually don't think Carey was bad for the tone of BF. But a Nolan Riddler could have been so awesome. I envision him as someone like Marilyn vos Savant, the highest IQ alive. He is known for being unstumpable, with a column or a tv/radio show where incredibly complex linear thinking puzzles are posited to him and he always manages to solve them.
After Batman becomes a fugitive, the Riddler is hired by the cops to find him. Knowing he's dealing with The World's Greatest Detective, he deliberately leaves a series of clues that lead Batman right where he wants him to go.
But taking the question as it is, I agree with Two-Face. Scarecrow a close second.