Per Wikipedia's respective entries for the following superhero films, these are the all-time top box office leaders that made over a billion:
The Avengers - 1.52 billion
Avengers: Age of Ultron - 1.403 billion
Iron Man 3 - 1.25 billion
The Dark Knight Rises - 1.085 billion
The Dark Knight - 1.005 billion
I don't think I missed any... But if anyone knows of a film that belongs in this tier based on the gross reported by Wikipedia, please advise.
I have no idea how accurate the sources for this figures are, just reporting them.
This article posted a year ago claims to have adjusted the grosses for inflation for the top 20 highest grossing superhero films, and if it is accurate it is a bit surprising.