I was completely enthralled with Highway to Hell when it came out -- it was the first true "rock" not "pop" record I loved (edit: second, actually, after Van Halen's debut). In retrospect it's not quite as good as I made it out to be when I was a young teenager. Back in Black was an absolute phenomenon -- I still remember when my local radio station teased and teased and finally played "Hells Bells" the day the record came out and it blew me away even without Bon Scott.
But looking back on their output now, I go back and forth between "Problem Child" and "It's A Long Way To The Top" as my favo(u)rite tune of theirs -- the bagpipes in the latter are so fucking funny and work so well it's hard to discount it, but the "Problem Child" riff is unstoppable, and that little spot about 2/3rds in where the tempo picks up slightly is just so, so good. At their best they are near the pinnacle of great old school rock n' roll bands and I can't see ever not loving them in whatever iteration of personnel they bring forth. Please turn your speakers up to 11, thank you.