1. An Unknown
I know this denies the whole point of having a list in the first place, but I think it's a possibility that bears consideration. The problem of having an established actor take over from one of the most iconic performances in cinematic history is that no one wants to be remembered as the second (or even third) best Joker. There's no dishonor coming third in a three man race but it's hardly great for one's legacy. Admittedly there would be even more pressure on an unknown - that level of trust and expectation - but such an actor would also benefit from the lack of preconceptions surrounding them: they could enter the role completely fresh, really make it their own. Then again, a juggernaut of a sequel like Batman v. Superman might not be the ideal testing ground for a budding young actor: anyone newcomer talented enough that the studio would trust them with this sacred greasepaint-wearing cow could easily be overwhelmed by the demands not only of the part itself but of a $200+ blockbuster in general. Still, if unknown quantities Henry Cavill and Brandon Routh could take on the Man of Steel himself, it's not beyond the realm of reason that there's someone out there who could do the same for The Joker. Beyond the histrionics that surround the part and the being one cog in a huge corporate machine, there's a lot there to work with and an actor with the lack of vanity to immerse themselves in it could certainly find something new to say about the scourge of Gotham.
And that about does it. Sorry to subject you to such a mass of text - my frequent digressions aside, I felt the character demanded it (hope you agree). There's no guarantee we'll be seeing the Clown Prince of Crime on the big screen again anytime soon: if they have to go for a villain in Batman vs. Superman, Snyder and Co. may well choose the more predictable, less attention stealing Lex Luthor. In the event they do go for The Joker, what do you think of some of the candidates above? Too predictable, just plain unsuitable? What do you think of Sam Rockwell who - thanks to Seven Psychopaths - almost made the list. Sooner or later, The Joker will make his return. All that remains to be seen is how he fits into the new continuity and how they set him apart fromwhat's come before...