I honestly think Nightmare would be a good place to start. Then Waking The Fallen (their best) and City of Evil.
agree with the first part -
Nightmare is the most varied of the A7X albums. what to do after that depends on what your favorite songs from
Nightmare actually are. off the top of my head, i would say something like:
"Danger Line" -->
City of Evil"Welcome to the Family" -->
Avenged Sevenfold"God Hates Us" -->
Waking the Fallenand of course, don't worry about the debut album until after getting everything else, even though it has a few really good tracks.