What I'm lovin' about this thread is that some people are serious and others are sarcastic - and the line is blurred between the two.
I like the idea of starting with "MacArthur Park" and working our way up.
Arrghh. Best song ever? It would seem that instrumental classics are not in consideration, only "songs" with vocal elements? I don't see any symphonies anyway.
My list, top 5 in no order:
Led Zeppelin "Rock & Roll"
The Who "Don't Get Fooled Again"
Nirvana "Smells Like Teen Spirit"
AC/DC "You Shook Me All Night Long"
The Ramones "I Wanna Be Sedated"
The most disturbing thing I've learned so far is that Cliff Richard was knighted.