When I say Zimmer's Joker theme/motif could've been better. I don't mean it should've been like Elfman's or Walker's (from B:TAS), which were perfect for their versions. I just think he should've done more with it. He gave Batman a dozen or so themes/motifs in BB. Joker could've used a few more motifs. I'll give Zimmer this he did capture the uneasy feeling of "chaos" and "anarchy".
But since you asked here's Elfman's "brilliant" Joker theme, which he only used 2 or 3 times in the actual movie. Really highlights Nicholson's twisted sense of humor, imo.