Not all X-Men are superheroes. Many mutants we've grown to know are survivalists, mercenaries, warriors, manipulators, and many more probably want to be left alone and pursue a career.
Still, the notion of a superheroic ideal to bend public opinion away from a paradigm that hates and fears them is a central X-Men tenet.
Who among the X-Men are the most "superheroic" in the obvious manner?
Storm, Nightcrawler, and Colossus jump out, but that's only the ANAD era. Sunfire could be seen as superheroic for an East Asian public. Beast, for his involvement in the Avengers... but he's leaning toward more of a shadow cabal idea man. Where Wolverine struggles with his villainous history, I think Rogue has actually moved through it to become an intentional heroine. Cannonball? Husk? Synch?