Those Alternative Tentacles reissues are essential no doubt. But the German released "Core" compilation from the early 1990's is even better because of the outtakes from the "Wait" EP recording session.
As most of you know, AOF represented the second wave of Chicago HC in the early 1980's and was often near fisticuffs with the more traditional first-wave bands, especially The Effigies. I am a fan of both bands but I think in hindsight, AOF was probably more consistent. I don't know if they ever reached the heights of "Below the Drop" but a lot of Effigies tracks just don't stand up over time. AOF, on the other hand, seems more relevant now than they did in the early 1980's.
I would say that any of the early AOF releases up to "Give Thanks" are definitely worth purchasing. Another great moment in midwestern punk/HC history.
Belfast
Poison In My Sweat
Dependence
Ghost In The House
Streetfight
Born To Be
By My Rules
Articles Of Faith
Sin And Redemption