It's always difficult to choose between so many extraordinary musical creations but let's try...
My #1 best song ever is
Protection - Massive Attack/vocals - Tracey Thorn.
I like the tune - perfect mix of sounds and spaces;
I like the
lyrics - written by Tracey when her husband Ben Watt was helplessly lying in a hospital bed, not knowing if he would ever come out of it
*Tracey and Ben were
Everything But The Girl - remember "Missing"?

*
And finally, Tracey's voice is an outstanding performance.
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I also have other #1's on different categories:
- Mozart's Piano Concerto No. 21 in C major - with a special mention of Movement 2 (Andante in F major), which raises my hairs all over like Beethoven does to
maggotbrain 
-
Anything by Nusrat Fateh Ali Khan (the only sounds that can really transport me into another world)