easy: Slayer. honorable mention to Black Sabbath and Metallica's work up to & including Justice. now they're just a bunch of top-40 hacks writing 3 minute made-for-radio songs based on one chord--listen to Orion, what a masterpiece with its complexity & flow; nothing like they're stuff now. Slayer is still kicking total ass after all these years. nothing compares to Reign in Blood!
