One extremely important piece of the melodic death jigsaw puzzle is the Gothenburg style, named after the city from which it originated. It is not certain what band originally started the Gothenburg sound, but it is widely accepted that In Flames, At the Gates, and Dark Tranquillity are the three major popularizers of the style, and some of the only widely known bands to practice it, with newer bands such as Arch Enemy and The Haunted being offshoots of Carcass and At The Gates respectively. -Wikipedia
I thought i can just give a little info. Not that you need it tho. Anyways so, which one is it for you? I guess this will end up Amon Amarth being the leader. I don't know maybe because they stayed pure from the beginning but my choice is Dark Tranquillity. They are giving the little signs of turning out like In Flames tho but i follow them!