Black was my personal favourite. He had a great menacing persona & you got the impression he just wanted to be as ruthless & unmerciful as possible. He also had a great look, even the face, although extremely hideous, was pretty terrifying.
Classic didn't do enough for me in the film, he was pretty much just there as a nod to the original. Granted, he was still badass, but he didn't get enough screen time, neither did the other super predators. Out of those two, I'd have to say I preferred Falcon, his fight with Hanzo was great & his mask had a very distinctive look.