WayoftheFist
Cold day in hell...
In my opinion you should start with the roots and work forward. Dig deep into Black Sabbath, Iron Maiden, and Judas Priest. Look at the big 4 from the 80's Metallica, Megadeth, Slayer and Anthrax (and throw Testament in there too just for being fucking awesome). To me those bands are still the best of the genre even though I like, and even love, a lot of bands that followed them. Also Pantera because Pantera is Pantera and Pantera was awesome. By the time you get there you should know what you really like. If you want to get into death metal and enjoy gutteral screaming there are better people than I to give you suggestions from that side of things. There are a lot of good bands that do that but it's never been my thing.