Quick talk about the Jokers.
Did you know that the history of the comics can be divided by 4 different periods, the Golden Age 1938 - 1950, Silver Age 1956 - 1970, Bronze Age 1970 - 1985 and Modern Age 1985 - TODAY, and in those divisions joker changed a lot?
When people say that prefer Cesar Romero, Jack Nicholson, Heath Ledger or Jared Leto, they actually are comparing all in the wrong way, and here is why.
BRONZE/MODERN AGE
The joker that most of people love in these days, just because he is the one in the comics that exploded in the pop culture, such as Killing Joke and the arc "Death of the Family" of New 52. Actually, he is the joker that everyone went to the theaters hoping to watch.
This joker is the one that have that strange "romance" with Batman.
SILVER AGE
That one is the goofy one, just a bank robber with sense of humor and a lot of gadgets, he had a joker mobile!
In the Silver Age comics could not have violence, and because of that we had this kind of villain, he was more a prankster than a nemesis to our bat detective.
GOLDEN AGE
Here is when things get interesting, almost nobody knows that Jack Nicholson was one Golden Age joker, and in that mater Jared Leto was too an Golden Age Joker, why? Both were the same, Jared Leto was just a reboot.
Look, in the gold age the joker didn't have that "romance" with Batman, the big bat was just a stone in the path, nothing more. Joker was a gangster, a cold blood killer that was only after the money, any means necessary.
CONCLUSION
To now on, when you talk about the joker don't just say that someone or something was bad, remember that every joker fall in one age, sometimes the writes just like more the golden or silver age before the modern, as you can see in this article of Cinema Blend where David Ayer, director of Suicide Squad, said and I quote:
I went back to the very first Joker comic. I think it was 1941 or something like that, which is also coincident with the first Batman comics. Batman the detective from the '40s had Joker as this insane gangster.