As others have stated, it's hard to single-out just ONE band. Take a look at the 1980s output of the selected artists below. This is NOT an easy decision (this only accounts for material RELEASED between 1980-1989):
Black Sabbath
Heaven & Hell; Mob Rules; Live Evil; Born Again; Seventh Star; Eternal Idol; Headless Cross.
Sure, the later few are weak, but the first 4 are pure genius!
Iron Maiden
IM, Killers, Number, Piece, Powerslave, Live After Death, Somewhere, 7th Son
Has ANY band, EVER, released such consecutive GREATNESS?
Priest
British Steele, Point of Entry, Screaming, Defenders, Turbo, Live, Ram it Down.
Priest, for all of their greatness, have always been spotty. A great record, then a weak record. They lack consistency. With that said, they STILL released 3 classics!
Queensryche
EP, Warning, Rage, Mindcrime.
4 of the decades BEST releases. They're right behind Maiden!
Metallica
Kill, Ride, Puppets, Justice.
Again, one can find little fault with these classics. It's only what came after.....that ruined things.
Ozzy
Blizzard, Diary, Speak, Bark, Sin, Tribute, No Rest.
Again, his 90s output was weak, and he's no longer the 'prince of darkness', but each of these releases is amazing!
Slayer
Mercy, Chapel, Hell Awaits, Reign, South.
'Nuff said.
King Diamond/Mercyful Fate
Nuns Have No Fun, Melissa, Oath, Portrait, Abigail, Them, Conspiracy.
Love his or hate him (the voice), the music is unbelievably strong!
TOUCH choice, indeed.