At the moment, it is probably "Seven Seas of Rhye" by Queen, or "I'm Looking Through You" by the Beatles.
Generally, my favourites are:
Like a Rolling Stone- Bob Dylan
For No One- The Beatles
The Village Green Preservation Society- The Kinks
London Calling- the Clash
Creep- Radiohead
Pinball Wizard- the Who
God- John Lennon
Ashes to Ashes- David Bowie
Sympathy for the Devil- the Rolling Stones
Ohrwurm- the Wise Guys (translates as "Ear worm", meaning "catchy hook")
Smuk Som Et Stjerneskud- the Olsen Brothers (translates as "Beautiful as a Shooting Star")
Strawberry Fields Forever- the Beatles
My Sweet Lord- George Harrison
Hallejuah- Jeff Buckley/Rufus Wainwright
Break on Through [to the other side]- the Doors
?Viva La Gloria? [Little Girl]- Green Day
I think that's a pretty comprehensive list. TBH, I could have added a lot more Beatles tracks (notably "While My Guitar Gently Weeps", "Good Day Sunshine", "Revolution", "Piggies", "Fixing A Hole", "Nowhere Man", "Norwegian Wood [This Bird Has Flown]", "Run for your Life", "She Said She Said", "Getting Better", "Help!" and the final medley on Abbey Road) and a fair few Queen tracks.