I can't pick just one, but I can name some of my all-time faves:
Vanden Plas - "Christ 0" Yes, I like it THAT much. If Vanden Plas gets any better, my brain will collapse. "Silently" might be the best song I have ever listened to in my life.
Queensryche - "Operation Mindcrime." Totally blown away by this disc for years.... That disc has an aura of it's own. Once in a lifetime release.
Dream Theater - "Images and Words." This release is what every prog release is compared to.
AC/DC - "Back in Black." I am soooo happy to see love for this here. Perfect sound and tone. EVERY song on the disc is great !!
Metal Church - "Blessing in Disguise." Despite pretty poor sound quality, this release just hammers from beginning to end.
Accept - "Metal Heart." All I can say is that if you haven't heard this, you are missing an arsenal of music !! This is intense metal that still sounds good.
Tesla - "Mechanical Resonance." This disc wouldn't have made this list until about 6 months ago, when I revisited it. I was blown away !! Great disc.
Angel Dust - "Bleed." What an awesome disc !! I still listen to it on occasion.
Bryant