Well, the first band I ever saw?
Mayhem, yeah the Norwegian Black Metal gods, weird, seen them the two times since they have been in Australia
Watain supported them the second time, was very cool.
Seen the staples of course, Iron Maiden, Lamb of God, Black Sabbath, Metallica, Megadeth, all that fun stuff
Been to the last five Sound Waves, some good some bad there though, all to taste I guess

Still, the best band I have probably seen is Alcest, so much love for them