The big 3 of DC is Superman, Batman and Wonder Woman.
But for you who are the big 3 of:
1. Teen Titans
For the classic Titans there's no big 3, but a big 5.
2. Villains of DC
Luthor, Joker, Darkseid
3. Among the xmen
Another big 5.
4. Among Avengers
Iron Man, Captain America, Thor
5. Among villains of Marvel Comics
6. Among heroes of Valiant Comics
Dunno.