Steeped as I am in comic book lore, it may be a problem related to an embarrassment of riches. My brain doesn't even want to go to some other medium where origin stories would necessarily be less epic. But which superhero origin do I pick? Examined with a "favorite" criterion, they all seem somehow lacking!
Superman's origin might as well be Moses'! Having your family killed was only ever fine the first time it happened, but then Batman's origin dovetails into a silly bat flying through the window. Wonder Woman mixes Greek myth and gun rituals and most unhealthy manner. Green Lantern... nobody thought it was strange for a flight simulator to take off? Flash's is entirely too convenient. Who let Firestorm's constituents walk into a nuclear reactor?! Oh and Marvel heroes? 80% of the ones not "born with them" (BORING!) are exposed to, or shot up with, radiation. So do I go for crazier, more convoluted, more obscure origins? Super stunt-suits melded to one's body by eldritch energies, that kind of thing?
You know what kind of origin I actually love? Heroes inspired by other heroes. All the 2nd/3rd generation guys from DC's post-Crisis era. I love that. I can relate to having a mentor and being a mentor, and it shows how a hero can have a major positive impact on another life. But that's not a very sexy answer, nor does it narrow things down enough for me to pick only one "legacy hero".
So here's my answer instead: Jonah Hex.
Ok, on the surface of it, it boils down to the dude getting hit in the face with a heated tomahawk and surviving with the "Mark of the Demon". Leaving aside the fact that THIS IS CLEARLY AWESOME, what I really love is the tendency Hex once had to invent all sorts of glib answers for people who dared ask about it. This trick was poached by Heath Ledger's Joker in The Dark Knight, but Jonah was there first! Here are a series of potential origins for Hex's scar from the Joe Lansdale Vertigo comics starring the character. Let me know which is your favorite.