Personally, I feel that Nicholason played The Joker better. I think he resembled the cartoon character much more then Keaton.
The Joker is a fictional character, a comic book supervillain published by DC Comics and appearing as an enemy of Batman. Created by Jerry Robinson, Bill Finger and Bob Kane, the character first appeared in Batman #1 (Spring 1940).
Throughout his comic book appearances, the Joker is portrayed as a master criminal whose characterization has varied from a multiple murderer to a goofy trickster-thief. He is also collectively the archenemy of Batman, having been directly responsible for numerous tragedies in Batman's life, including the paralysis of Barbara Gordon and the death of Jason Todd, the second Robin.
Throughout the character's long history, there have been several different origin tales; they most commonly depict him as falling into a vat of chemical waste, which bleaches his skin and turns his hair green and his lips bright red, giving him the appearance of a clown.
The Joker has been portrayed by Cesar Romero in the Batman TV series, Jack Nicholson in Tim Burton's Batman, Andrew Koenig in the 2003 Sandy Collora fan film Batman: Dead End , and Heath Ledger in Christopher Nolan's The Dark Knight, for which he won an Academy Award for Best Supporting Actor. Larry Storch, Mark Hamill, Kevin Michael Richardson and Jeff Bennett have provided the voice for the character in animated form.
Wizard's list of the 100 Greatest Villains of All Time ranked the Joker as #1
Gotta love that smile!