Ra's al Ghul, because I think a film with him as a central character has a lot of potential. They could for instance do a film highlighting his background and origin as a man who has lived for centuries and has seen the world change thanks to the regenerative qualities of the Lazarus Pits. A background similar to that as revealed in the Batman: Birth of the Demon TPB.
Red Hood is the obvious choice since he's more anti-hero than villain, but I went with Harley Quinn because I think she could carry a film with a few key supporting characters, either a Gotham Sirens setup or the Suicide Squad setup. Come to think of it, Amanda Waller probably counts as a Batman villain still, give her a film.
Guess I'm the only one to vote for Hugo Strange haha. Hugo Strange is such a mysterious character to begin with for me. I think he's the type that would definitely have enough story line to get divulged in. I do agree a Poison Ivy and Harley Quinn movie sounds amazing though! Mad Hatter was tempting too, but good old Jervis doesn't seem like he has enough back story to make an entire movie out of, no matter how much I love the villain.
Catwoman deserves justice. Think of where that character would be now if they made a good Catwoman movie instead of the one they did make.
There is a lot of interest in this character, and a lot of story telling potential. I like the heist idea.