In his book, Supergods, Grant Morrison argues that Superman and Batman are opposites:
“Batman, then, may have been a construct, but he was an immaculate construct, precision engineered to endure. Batman was born of the deliberate reversal of everything in the Superman dynamic: Superman was an alien with incredible powers; Batman was a human being with no superhuman abilities. Superman’s costume was brightly colored; Batman’s was grayscale and somber with mocking flashes of yellow. In his secret Clark Kent identity, Superman was a hardworking farmer’s son who grew up in small-town Kansas, while Batman’s Bruce Wayne enjoyed life as a wealthy playboy—an East Coast sophisticate descended from old money. Clark had a boss; Bruce had a butler. Clark pined after Lois; Bruce burned through a string of debutantes and leading ladies. Superman worked alone; Batman had a boy partner, Robin, who wore green briefs, a black mask, and a yellow cape. Superman was of the day; Batman was of the night and the shadows. Superman was rational, Apollonian; Batman was Dionysian. Superman’s mission was the measured allotment of justice; Batman’s, an emotive two-fisted ask-questions-later vendetta.
Superman began as a socialist, but Batman was the ultimate capitalist hero, which may help explain his current popularity and Superman’s relative loss of significance. Batman was a wish-fulfillment figure as both filthy-rich Bruce Wayne and his swashbuckling alter ego. He was a millionaire who vented his childlike fury on the criminal classes of the lower orders. He was the defender of privilege and hierarchy. In a world where wealth and celebrity are the measures of accomplishment, it’s no surprise that the most popular superhero characters today—Batman and Iron Man—are both handsome tycoons. The socialist and the socialite, the only thing Superman and Batman could agree on was that killing is wrong.”