They're still Joker. They all have the same constants. Green hair, white face, red lips, purple suit.You got Cesar Romero's version of The Joker, the Mark Hamill's version, Jack Nickolson's version and Heith Ledger's version. They're all the same character but they're portrayed quite differently. If you want a version that best portrays The Joker then I'd say it's Arkham Asylum's joker voiced by Mark Hamill. He's like a mix of all the previous jokers as well as his own version.
There can't be a single defining take on the character because that's not how the character is written.
All Joker's are still the one Joker.