Superman and Batman are best friends
In the wake of the latest movie (which I have yet to see, more or less out of familial loyalty) with unnecessary conflict, Nate Silver’s website of science leaps over a tall building to insist that Batman and Superman indeed enjoy the oldest bromance in serial fiction. Regardless that it’s more popular among certain creators to insist there ought to be a personal friction between the two heroes (the source of which I’m loath to explore), FiveThirtyEight studies the actual numbers of shared appearances between different heroes and Superman or Batman. The pairing of the two occurred more often than pairings between Batman and any Robin.
Mind you that’s because Batman has had multiple Robins, each partner a separate character with the same name and for long stretches of time the Batman was a solo hero with Robin fighting crime by himself. Consistently across time, space, and the multiverse Superman and Batman cannot resist teaming up.