While all the Losers nurse varying degrees of crushes on Beverly in the book, it's always Bill and Ben who seem to love her the most. While the child version of Beverly is more drawn to Bill in both the book and the film, her preferences as an adult depend on which version of the story you're following.
In the book, Beverly and Bill succumb to their mutual attraction, sleeping together in Bill's hotel room the night before the Losers go down into the sewers to battle Pennywise. But in It Chapter Two, while the adult Beverly does seem to oscillate between the two for a while, she ultimately chooses Ben, sharing an underwater kiss with him while the Losers celebrate their final victory. Later, after the Losers leave Derry, it is revealed that Beverly and Ben stayed together, and their final shot sees them happily preparing to set sail on a boat.