I don't know if you can put a specific cut off for issues or dates. I grew up reading the latter part of Englehart's run and Shooter's first run and that's what I think of as Avengers. But in between those two were some clunkers, I think by Conway. And after 177, which was the conclusion of the Korvac saga and where they peaked for me as a kid, I didn't care for what came after that for a while.

Stern's run, which I read in college when I got back into comics for a bit, wasn't bad as I recall. I've only read sporadically since then but there was a decent story line in the 90s, I think by Bob Harras, called Galactic Storm. The Busiek run wasn't bad. After Bendis took over there were so many titles, it depends on what you want to call "The Avengers." The writing was very good on a lot of them but, having grown up on the bronze age Avengers, when I read many of the Bendis era books I'd find myself shouting "That is NOT the Avengers!" I find myself doing that even more vehemently with the movies (which really isn't an appropriate thing to stand up and shout in the theater).