I'd rather argue about god, but...

Master of Puppets
Holy Diver
Powerslave
Number of the Beast

Holy Diver is a good one.

My bro went to a Dio concert once and Bruce d***inson showed up on stage to do Rainbow in the Dark apparently. What the f*** is that.

I did get to see Queensryche, Halford, and Iron Maiden all perform in one night though. That was pretty goddamn sick.

What I consider just metal it would be

Metallica's Master of puppets

there are others but they fall under different metal or rock categories. When I think of just metal, its Metallica.

Massacra - Final Holocaust
Morbid Angel - Blessed are the Sick
Suffocation - Effigy of the Forgotten
Atheist - Unquestionable Presence
Morpheus Descends - Ritual of Infinity
Immortal - Pure Holocaust
Immortal - Sons of Northern Darkness
Emperor - In the Nightside Eclipse
Darkthrone - Transylvanian Hunger
Bathory - Blood, Fire, Death
Beherit - Engram
Mayhem - De Mysteriis Dom Sathanas
Absu - Tara
Averse Sefira - Advent Parallax
Antaeus - Cut Your Flesh and Worship Satan
Antaeus - Blood Libels
Gorguts - Obscura
Gorguts- From Wisdom to Hate

I can not choose just "one" best of all time and there are way more out there that are quality releases and should be mentioned, but these are the standards that I always seem to go to.

Edit: I forgot Shovel Headed Kill Machine by Exodus