Heavy doesn't hide behind 15 minute guitar solos, mach 5 double bass, or singing about scooping brains out. Those are mere gimmicks. Heavy is heaviest when it comes and goes before you know what hit you, allowing some time to linger before you listen again. Like a punch in the face.
Heavy can't be too polished. Hair bands aren't heavy, and neither is a spinning drum platform. No, heavy is simple, brutal, and crude. A heavy song should feel like a rat rod, and sound like one.
Heavy isn't a 50 section 17/5ths epic. Simplicity is key, and if there are odd time signatures or other complexities, as there are in some heavy songs, they shouldn't distract from the overall heaviness.
Heavy isn't vocals so distorted that you can't tell the difference between the voice and the guitar. Or that it's even a human singing. Vocals are heaviest with enough humanity to empathize with what's being sung and who's doing the singing.
Finally and most importantly, heavy has no rules.
So without further ado, here's the Townhouse list of the heaviest songs around (probably not all of them, but it's not a bad place to start). Hang on to your hats.