The title pretty much says it. It doesn’t have to be just your favorite guitar playing in a 70s heavy album, just the album you like listening to the most that’s heavy metal.
This is a tough choice. I like Black Sabbath a lot. Tony Iommi was the master of the riff and had tremendous influence over the metal guitarists from then on - even to today. Still my pick is Sad Wings Of Destiny. Great songs, guitar playing that really complimented the songs, and amazing vocals from “the metal god” Rob Halford.