Batman: Dark Victory
One thing that the Marvel Cinematic Universe has done more frequently than its DC counterpart is repurpose the titles of certain stories while not making a straightforward adaptation of said comic. That was the case with films like Avengers: Age of Ultron and Captain America: The Winter Soldier, which made liberal changes to the source material while still utilizing the distinctive title.
That would give the upcoming film a wealth of potential titles, though something moody like Dark Victory would probably work best with the confirmed tone and style of the film. The original comic centered around a mysterious murderer called the Hangman targeting criminals around Gotham City. The broad strokes of that murder mystery falls in line with what Reeves has confirmed will be the focus of the film. Even if the film doesn't follow the plot of the original story (which was partly focused on the origin of Robin), the title could still be appropriate for a dark and moody mystery starring Batman.
Batman films have always been somewhat defined by the villains who appear in them, but a quote from Reeves hints that he wouldn't just want to use just one of the iconic bad guys. "There will be a Rogues' Gallery. The casting process will begin shortly," explained Reeves in an interview with THR. "We're starting to put together our battle plan. I'm doing another pass on the script and we'll begin some long-lead stuff to start developing conceptual things."
This all suggests that, while the film could have a main villain at the center of its mystery, there also could be a number of other members of his rouges' gallery set to appear in the film. Calling the film Rogue could put the focus on the various villains of Gotham City. With the Penguin rumored to be the main villain of the film, Oswald Cobblepot could easily be the kind of villain who would assemble a full group of enemies to confront Batman, and the title could draw on that by focusing the title around the rogues in question.
Batman: Gotham City
While speaking to THR, Reeves said, "I'd love this to be one where when we go on that journey of tracking down the criminals and trying to solve a crime, it's going to allow his character to have an arc so that he can go through a transformation." Such a focus on the specific criminal aspect of Gotham City could give Reeves a reason to name the film after its iconic setting.
If Reeves follows through on his plan to make the film more focused on the crime than the villains, then it would make more sense to name the movie after the dark cityscape the film takes place in. Gotham City is often described as a character in it's own right. Centering the narrative around Batman during the course of an investigation, taking him throughout the city as he tries to solve a mystery would fall in line with all the reports about the rumored plot of the movie. Naming the movie after the city could fit perfectly with that tone.
Matt Reeves' The Batman is scheduled for a Jun. 25, 2021 release date.