There has always been a bit of shared leadership between Superman, Batman, and Wonder Woman over the Justice League in the comics, and that same dynamic might also play into Warner Bros. DC Cinematic Universe.
A recent conversation between Batman V Superman: Dawn of Justice actor Henry Cavill and Jimmy Kimmel revealed that there is some disagreement between Batman and Superman as to who is the de facto leader of the group.
"Cavill: There's pretty much an argument between him and Batman as to who is the leader.
Kimmel: But they're always fighting these two. I think there's a lot of sexual tension between the two of them
Cavill: yeah, and Ben is a beautiful man
Kimmel: Haha, wow, that would be the greatest porno ever!"
While we know in the seeds are planted for the League in Batman V Superman, we still don't know who ultimately comes up with the idea, so that debate will have to wait until March 25th when the movie opens in theatres. That said, don't count out Wonder Woman from that mix either. She is just as important to the group as they are.