For proficiency I have to hand it to Suicmez. For volume of work, Azagthoth has put out more good songs in total. For influence, Schuldiner put the whole thing on the map and reinvented it after that.
I can't say I really have a favorite, so I'll say myself. According to my itunes, my favorite death metal band is Carcass, with the most high rated songs. Dies Irae, Death, Noumena and Arch Enemy make up a good portion too though.