I am partial to
Hellhammer Apocalyptic raids or Celtic Frost's
Morbid Tales. Great early stuff
There are literally 1000's of DM/BM bands but only a very few stand out. I would also have to give a nod to Venom's
Black Metal, Bathory's The Return and Possessed's Seven Churches
Back in the day (I am 45), these bands were not lumped into sub genres, it was death/black metal all grouped together. Sheer heaviness and crushing atmosphere were all that was required
Always buyiing rare and private release Metal