An unknown.

Perfect! By far the best out of these!

Helena Bonham Carter is a phenomenal actress with a wide range of character. She can play characters that other actresses can't. She would be phenomenally spectacular in the part of Harley Quinn. I think she would get the part with no problem.

She would be so perfectly crazy! That part would fit her so well!

Helena Bonham Carter all the way! This part would fit her perfectly! Helena is great at playing these characters. She'd make Harley a vicous animal straight out of the zoo.

Ewwww how could you choose Kristen B.?

I'd love to see Helena as Harley, she would be perfect for her! ^^

I LOVE KRISTEN BELL!

I love most of her films. She is a powerful actress who is perfect for almost any role. She can play parts that these other actresses can't.

I actually did a real long process casting for Harley (She's main villain in my fanfic) and chose Sarah as the perfect Harley

Helena knows how to make a really crazy performance.

I think that an unknown actress would be better

none of these really :/