While the DC Comics Free Comic Book Day issue features an all-new story by Geoff Johns and Jim Lee, in addition to a 2012 preview, Marvel Comics, on the other hand, is offering a reprint of last year's Avengers #12.1 by Brian Michael Bendis and Bryan Hitch.
Well, not exactly "Avengers #12.1," as it turns out Marvel is renaming the book to "Avengers: Age Of Ultron #0.1" for FCBD.
I think when Tom Brevoort was questioned about the reprint being rather lame ('cuz it is!), Brevoort responded that it was an important issue or something.
Turns out it might be just that, as Bleeding Cool notes, the Age Of Ultron storyline is probably Bendis' next big story. And we just saw that in Marvel's "Point One" issue as well.
Here's the new cover, which is specific for retailers to use and promote when they order enough (via BC and Third Eye Comics):