Let's go back in time. In the 60's, a revolution took place in the music stage, taking it to another level. An heavy level. Iggy Pop and a bunch of other crazy dope aliens had already sent a serious message, but the real pioneers, were yet to come. This newcomers, were about to change things again... Ya'll know who they are so let's cut to the chase.

These are all pre-1975 albums. They belong to bands that, in a way or another, helped the heavy metal growth in mid-70's.
I want to know which one of them makes the best debut overall. Which one made its band start its career off the best? Which one contributed the most to the evolution of heavy metal from hard-rock?
I choose the Led Zeppelin's one, not only for personal reasons, but also for Plant's vocal skills, the guitar riffs, and that instrumental drum track... I find it a fun record, and i really think that music was ahead of its time. IMO it's their best record, and the big responsible for hard-rock/heavy metal launch, side by side with black sabbath's two first ones. If i had to choose a 2nd one from the list, i'd go for the Judas Priest debut. I just love the mixing of blues, rock and hard-rock they did there. An highly underrated record from Priest's hard-rock era.