"Believe In Nothing" (not only for the music, vocals and arrangement but also for the lyrics), closely followed by "We Disintegrate" and "Insignificant Am I".
I chose "Believe in Nothing", but it BARELY beat out Sound of Silence. I'm not much for covers, but it took me 3 full listens to figure out what song it was(although, I AM a moron). IMHO, that's how cover songs SHOULD sound.