My choices for the best hard rock albums of all time would be different now than they were then, I expect, and given that I was deeply into the genre at the time, perhaps my teenaged choices would be more significant. Looking back, the albums that I was fondest of at the time were probably (roughly ordered by descending preference):
Led Zeppelin - Physical Graffiti
Pink Floyd - The Wall
Rush - 2112
Black Sabbath - Volume 4 or possibly Sabotage
Boston - Boston
Aerosmith - Toys in the Attic
Blue Oyster Cult - Some Enchanted Evening
Deep Purple - Made in Japan
Van Halen - Van Halen
Ted Nugent - Double Live Gonzo
AC/DC - Back in Black

As I grew older, some of these bands lost their appeal rapidly, while there are others that I can still listen to happily. Also, I discovered The Who rather late for some reason, so although I didn't listen to them in my early years, they became my favorite band in university. And although I did consider Pink Floyd to be hard rock in those days, I would not include them in that category now. If I had to list the top 5 today, I would go with:

Led Zeppelin - Physical Graffiti
The Who - Who's Next
Blue Oyster Cult - Some Enchanted Evening
Boston - Boston
Aerosmith - Toys in the Attic

By the way, I realize that I'm omitting some of the usual suspects - Jimi Hendrix and Cream for example. I'm deliberately skewing this list toward my own personal favorites, rather than the albums that I think were most significant.