The two are very different, but I'm not sure if one is really better than the other, in my opinion. In both versions, Harley is devoted to Ivy, but in the DCAU, Ivy sees Harley as little more than a stooge that is occasionally fun to hang around with, whereas in the DCU, Ivy genuinely likes Harley, and has often helped her out of a tight spot. They're both interesting relationships, but I admit to a slight preference for the DCU version - the original is pulled off very well, but it strikes me as a bit of a rehash of the Harley/Joker relationship.