I am a fan of both of these bands, Although Metallica is great i am leaning towards S.O.A.D. They're music is much more diverse and quirky unlike any other band. The fusion of Serj Tankian and Daron Malakian bring it all together. I must admit, i've been reading much of these comments and i would have to disagree on some of what is being said. System of a down is in no way any less serious then Metallica, i see people writing comments like "Soads songs confuse me, they are funny" almost every system of a down song is about the Armenian Genocide and politics. The so called "funny songs" are all metaphors for war. Alot of other bands would prefer to stay away from the political side of things to prevent their fans from listening to them. Don't get me wrong i love Metallica and they will be forever one of the best bands of all time but System of a Down in MY opinion is an outstanding band that is unique in it's own way which takes the cake for me.
System of a Down, for me. 2005 was the year of System in my life, and I'll never forget it. Metallica has few memorable hits for me, and as Frostbite said, SOAD really seemed to be on some sort of personal crusade to get the word out about the terrible things that happened to their people. I was really impressed by that, and it was one of my first real doses of reality upon graduating from high school.