What is the heaviest sub-genre of metal?

I guess it's a matter of opinion. Some will say Black Metal, but Death Metal has a much thicker, heavier, more guttural sound in the vocals. Deathcore is pretty heavy too because they have deathgrowls, shrieks, blast beats, double kicks, way down tuned Guitars, you name it.

But when it comes down to it, the factor that makes them more extreme isn't the sound. It is the ideology of the band and the way they express it. Gorgoroth kicks everybody's a**

yes, it's based on opnion but Children of Bodom kicks everyones a** no doubt about it.