I'd pick either;
'Imagine' - John Lennon = I know some people might think it's typical and cheesy to pick this one but the words are just incredible. It is perfect. Imagine if there was no religion or country, how much peach could there be in the world?
my second is:
'teenage kicks' - The Undertones = Not just because it's one of my favourtie songs and also lyrically brilliant, but I would have loved to have affected a great man like John Peel like this song did. One of the most amazingly musically minded people ever to walk this earth and I would have been proud to affect him so strongly.
But what about you?