Finally completed my run in 2016 with a trade for #1 (and a spare #4). Gave up a stack of 18 books from Gold to Bronze, probably highlighted by an ASM 129. But I am complete. It is my all-time favorite title, and I will read it straight through before ever parting with it.
My favorite story arcs in addition to the obvious classics are the Korvac saga, the Count Nefaria trilogy, and the long Masters of Evil storyline that culminated in #275, off the top of my head.
Avengers #4 is probably my favorite book, and the last one I will part with, along with Flash 123, if I can help it. To me, they symbolize everything I have loved about comics with the melding of the golden age history into the silver and thus the rise to prominence of continuity.