From this list...
Best Heavy Metal album of the 70s: Black Sabbath - Paranoid (very close runner up, Judas Priest - Hell Bent For Leather)
Best Rock album of the 70's: (TIE) KISS - Destroyer / Van Halen - I
Best combo (Metal/Rock) album of the 70's: Deep Purple - Machine Head
Choose one single album in the entire bunch!? Egads