Why?
Both analogies are pretty heavy handed and obvious but Carnival Row makes more sense.
The police in both universes are kind of shit. That makes sense in Carnival Row. It's a parallel time to World War 1 Britain. Crime investigation is in its infancy. The police are racist or "specist" or whatever. Corruption is a way of life for the police. Our hero, Philo, presents us with the modern view. He also brings with him investigative techniques we recognise and genuine engagement with the community he hopes to protect and serve.
The opposite seems to happen in Joker. It doesn't make sense in Gotham, or at the very least it isn't explained. Why are the police so shit? Why do two detectives go alone after a suspected murderer who is acting erratically? They think he shot three people and presumably have an eyewitness report of a fourth murder. Yet they shout to attract his attention from a great distance. At a protest when a cop is pushed he dives over a barrier to fist fight the protesters. He's just stupid.
The crucial point of the tension in Carnival Row is when the Prime Minister dies. This isn't the fault of the Fae but it represents a moment of emergency and panic where the government can pass bills and measures to crack down on the perceived enemy. This feels pretty true to life. Suddenly being racist is fully government sanctioned, not only that but dressed up as necessary to the safety of the state.
In Joker's Gotham three of it’s more affluent citizens get shot. It's after a bit of a clusterfuck but the media spin it as the start of something. Somehow that something happens. In real life we've seen city wide riots after single incidents, for example Rodney King, but usually the rioters are on the side opposite those who just beat or killed someone. It makes no sense that what is portrayed as a vicious and tragic killing inspired people to riot for what? The riot to kill more rich people.
In terms of characterisation , Philo’s reliable and more likable. He bridges the two factions and ,while philosophically, you know racism is bad it's easy to understand why people get into it (spoiler, because it's easy).
On the other hand, Joker is an unreliable character who is also pretty unlikable. He's been dealt a shit hand and everyone else in his world is hardly understanding of mental health. His viewpoint doesn't explain why the city is in flames it only shows what happens around him. The movie paints the downward spiral as a reaction to Joker rather than Joker being just a thing that happened in much larger spiral. In the world of Joker those people would be rioting anyway but because of him they wore Joker masks instead of Guy Fawkes masks. In essence the film is incomplete in a way I feel matters due to this central gap in logic. Carnival Row satisfied me much more.
Obviously you should watch Carnival Row. Should you watch Joker?
Yes. It's getting big press because Intelligence Agencies are warning about potential shootings in America, doing exactly what the media did in the film. Joaquin Phoenix is grotesque. The colour palette is grim. Batman or the mythology of Batman doesn't mess up the story. There's some good tension, made more interesting when you imagine viewing the movie in a climate of immediate danger.
My big caveat is have something nice planned for after. I went blackberry picking. The grass was green, my dog bounded around, and the evening sun was warm until I got back to a warm fire.