I only have 6 AC/DC studio albums, so on the basis that I'm obviously not going to vote for records I never heard, this one is easy!!...
Back in Black
For Those About to Rock
Highway to Hell
Black Ice
Let There Be Rock
They are a far better live band than studio band IMO, I get no sense of the energy or excitement with their studio recordings that I get when I see/hear their live stuff on record or DVD, 'Live' (1992) is outrageously good, one of THE albums to buy of all time to test drive a new mega-watts stereo system.