Throwdown: The Return of the Sinister Six VS Spider-Man: Blue
Structurally, these are two similar stories. Both are six-parters (that remain in print, and have appeared on lists of the best Spider-Man stories) although many of the individual chapters can be enjoyed independently.
David Michelinie and Erik Larsen's "The Return of the Sinister Six" (Amazing Spider-Man #334-339) featured the second appearance of the villainous team from the first annual, bringing them back as mainstays of the Spider-Man comics.
Jeph Loeb and Tim Sale's "Spider-Man Blue" focused on the beginnings of Peter's relationships with Gwen and MJ.
Which story do you prefer?