Heath.
Jack's 'Joker' was great, can't deny it. But Heath became the Joker (which unfortunately, led to a terrible end). No matter how much you tried to look past all the make-up, you only saw the Joker, not Heath. And he portrayed the character as he really is - a dark, twisted, unfeeling psycho. Jack's portrayal was still a bit too 'light' for me.