This entry compares the two contemporary Batman movie incarnations of the Joker. By contemporary, I mean that Cesar Romero will not count in this entry. Jack Nicholson played the 1989 Joker in Batman. The late Heath Ledger played the 2008 Joker in the Dark Knight.
First, I'll just state my thoughts on the 1989 Joker. He's certainly colorful and comical. I do like that he's a bit more "light" in terms of humor than the "Dark Knight" Joker was. Also, he's a bit "classier" and a bit more of a "ladykiller" than the "Dark Knight" Joker.
Now, I'll give my thoughts on the "Dark Knight" Joker. Wow...this Joker actually belongs more in a horror movie than a Batman movie. His hair looks more disheveled and his makeup and scars make him look more of a monster than the 1989 Joker. His demented, violent, chaotic personality in the movie only further cements that fact. Needless to say, this is a person you wouldn't want to run into in a dark alley.
However, nowadays, many people seem to like Heath Ledger's Joker better than the Jack Nicholson Joker.
This poll from Faniq.com states that people like Heath Ledger as the Joker more than Jack Nicholson.
This poll from quibblo.com also states that people like Heath Ledger more.
On googlefight.com, there are more results for "Heath Ledger Joker" than "Jack Nicholson Joker".