I actually voted for the 1970s and 1980s.
Even though the 1970s were before my time (born in 1979), a lot of that decade's music is really good. And, since the 1980s were my childhood, it's no surprise that I would vote on 1980s music since it brings me back to my childhood when I hear it.
Edit: Of course, there is some good music in many decades before the two I've chosen. 50s and 60s have some good songs that I like. And, let's not forget classical music from many decades ago.