Tied between Mastodon (progressive sludge metal) and Rings of Saturn (technical deathcore so let's get that autistic screeching about it outta the way) and neither is of my most favorite metal genre rn (but they come close just as prog metal), post-metal, which melts numerous separate heavy metal genres together. If I could pick one, there'd be three bands sharing the first place. It'd only get really crowded and I'd have to put them in order, which I can't.
One band does black (dark ambient, black doom, blackgaze, post-BM, atmospheric BM), another doom (seen sludge, stoner and drone doom most commonly), another "just" post-metal (like Neurosis or Pelican), another industrial, another prog, tech or djent, another shoegaze (hence the other name for the genre, metalgaze) but in post-metal, these no longer have well-defined borders, they dissolve together, and post-metal itself is not so easily defined.
In reality, I have dozens of true favorites from several subgenres of metal. All have their place and tend to fall under progressive, extreme or industrial metal. Metal is life, really.