I just picked up a copy of Back in Black a few weeks ago, the vinyl edition. Bon Scott will always be my favorite Acca Dacca vocalist, but Brian has grown on me over the years.
Two legendary bands, two great records it's hard to pick between them. If IV wasn't so overplayed then I would pick it, but it's only the last few years that I've stopped listening to radio that I can play it and enjoy it properly again. I suppose you could say the same for B in B too come to think of it.
I might be wrong but I think B in B has outsold IV, it is in the top 5 best selling albums of all time, if I'm in error someone with more knowledge can correct me.
After saying all that,,,I abstain.