The first actor I have in mind is no other than the riddler himself, Jim Carry. Jim Carry's performance as the riddler in Batman forever was simply incredible in my opinion. You would be hard-pressed to find an actor as talented as Jim Carry.
My next choice is the best out of 12, The 11th DOCTOR MATT SMITH! I honestly can't decide between these two on who would do it better. Matt Smith may be the best choice for the joker. We have seen Matt Smith act both super silly and super threatening and I think he could bring those two things together and become the best joker ever, even surpassing Heath Ledger (May he rest in peace)