I voted slipknot, but I love pantera, and I like allot of the other groups that the other posters are mentioning, I do however HATE metallica IMO they are just as over rated and I think even more so than other people think slipknot is over rated!! slipknot has an authentic style, are much more entertaining and overall I think there music is allot better than that of metallica..
I must admit my all time favorite band is "RAGE AGAINST THE MACHINE" I don't know if you would consider them a true metal band? but in the name of intensity, music, lyrics, importance (politically), and authenticity there are few bands that can match them in all aspects of what make a great band!!
I also love BLACK SABBATH, MARILYN MANSON, and so on etc..etc.. there are so many variables to picking favorite bands cuz some are nostalgic, some are contemporary, so allot of bands are liked or disliked due to the era they were in there prime or when they debut'd, so I love allot of metal bands.. most are of the commercial variety, I have not delved into the underground bands that recieve no radio play due to graphic content, but if it sounded good I would be a fan of that as well..
I absolutely love heavy metal!! so no matter the kind of metal it is, speedcore, black metal or whatever they call the underground stuff thats never heard on the radio I am sure I would like it if I heard them.. but I don't have the financial capacity to buy all that undergroud music..
I am sorry for this long disertation but I am very passionate about my music!! I love music as much as girls and guns!! my musical diversity is all over the map.. you couldn't pin point my ear for music even if you knew me..