Thanks to my return to the Apple family in 2002 and continuous smooth migrations from Mac to Mac since then, I now have a certain degree of continuity with my music collection management.
There's been a small amount of lost information due to things like tracks being replaced when I've switched from a mix from a friend or a 'best of' album to the original, but in general these are the same tracks I've had all along.
One big factor in that array of music is my habit of weeding out things that I don't like. 'Meh' doesn't cut it; a song has to be rated three stars or higher to stick around for long. Each time a track irritates or bores me (and I know it isn't just a temporary mismatch in mood), I drop it one star. If it's already down to a single star, I delete the track. This means over time, some albums and artists completely vanish, but allows me to listen to my music on shuffle play with little risk of bad songs.
The track with the most plays in my collection is, somewhat oddly, My Chemical Romance's version of "Desolation Row" from the Watchmen soundtrack, but that's a result of it being played on loop as the writing background to some action scenes I was writing in a fiction work in progress and doesn't thus reflect my general listening habits.
With it set aside, my top twenty songs are:
"As Serious As Your Life" by Four Tet (electronica)
"Wildest Pig In Captivity" by John Renbourn (folk)
"Stiff Jazz" by Dzihan & Kamien (electronica)
"Cashmere" by Nerf Herder (alternative/punk)
"Time Has Told Me" by Nick Drake (folk rock)
"Northern Sky" by Nick Drake (folk rock)
"Vaseline Machine Gun" by Leo Kottke (folk)
"['casino' from the game Grim Fandango]" by Peter McConnell (big band)*
"Hey Bulldog" by The Beatles (rock)
"A String of Pearls" by Glenn Miller (big band)
"You're The One I Want In The Next Episode" by Grease Vs Dr Dre & Snoop Dog (mashup of 50s-esque and hip hop)
"YYZ" by Rush (rock)
"Cobbler's Jig / Maltese Brawls" by John Renbourn (folk)
"Pyramid" by Backini (electronica)
"Polythene Pam" by The Beatles (rock)
"Espionage" by Green Day (lounge/rock)
"Bucephalus Bouncing Ball" by Aphex Twin (electronica)
"The Earthly Diana" by Combustible Edison (lounge)
"Lark in the Clear Air" by John Renbourn (folk)
"Peter Gunn" by The Art of Noise with Duane Eddy (electronica/rock)
The oldest albums in the collection for which I still retain over six songs are White Courtesy Phone by Angel Corpus Christi and Ego sum Resurrectio: Gregorian Chant for the Dead by the female vocal ensemble Aurora Surgit. The latest album added was Let It Bleed by The Rolling Stones.
Yes, it could be said that my taste is a trifle eclectic.
*To my utter delight, in looking up the name of the Grim Fandango composer just now I discovered an entire sountrack album available! O bliss!