Assuming you're going for excerpts from an ongoing series, I'm tempted to go Season of Mists from Sandman, but you have to follow your heart:
Avengers 164-196 + Avengers Annual 7-9 + Marvel Two-in-One Annual 2 from October 1977 to June 1980 is the greatest run of issues in Marvel's mightiest title.
John Byrne, David Michelinie, George Perez, Jim Shooter, Jim Starlin, and company bring you the Beast, Black Panther, Black Widow, Captain America, Falcon, Hawkeye, Hercules, Iron Man, Jocasta, Moondragon, Ms. Marvel, Quicksilver, Scarlet Witch, Thor, Vision, Wasp, Wonder Man, and Yellow Jacket.
It starts with Shooter and Byrne serving up
Nefaria and the introduction of Gyrich. Starlin's
Thanos! The all-hands-on-deck
Ultron story and the legendary
Korvac Saga. Michelinie-Byrne awesomeness including the
Yesterday Quest. Classic down-time issue 189. Arsenal and some Stark History. The classic government hearing. And the George Perez
Taskmaster issues to cap it off!
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A poll on the Avengers Forever Facebook group a few years back had this top five (with #5 included in my selection above)
#1 Under Siege (1986-1987)
#2 Avengers Forever (1999-2000)
#3-4 Kree/Skrull War (1971-1972)
#3-4 Avengers/JLA (2003-2004)
#5 Korvac Saga (1978)