Maybe suggestions should be included in this list:
https://en.wikipedia.org/wiki/List_of_best-selling_singles
At least 5 million sold?
I second the vote for 10cc I'm not in love
and crimson & clover.
But it is my perception that this thread is not about somebody's all time vote for the best single song of all time, extracted willy-nilly from any album or wherever one pleases.
The thread title itself immediately conjured up in my mind the question of how sometimes, there are music lovers who might never have purchased a cheap 7" styrene 45RPM single might be moved to buy one, just because a popular hit single is (maybe coincidentally) so uniquely special to them too.
Besides, if any hit single song were really that good, I would expect that the album version be better fidelity and include other perhaps even more interesting songs that don't get played on the radio, and as a bonus, album versions can be and often are longer with more content.
I have always been most strongly motivated to buy LP albums, open reel @7.5 IPS, Compact tape cassettes and various digital discs (CDs, SACDs etc.), but 45s always struck me as virtually worthless junk, far below even the worst cheap, no-name, low grade 8-track cartridges.
So here it's all about pop-chart topping single songs sold in the millions on physical 7" 45RPM plastic discs.
Perhaps add in multi-million selling digital copies if they were presented to the public in that clickable purchase format.
A nice idea this thread, because easily 90% of my music collection would be wholly unknown, unknowable, and if they were exposed to it, something to be avoided at all cost to more than 90% of the music purchasing masses, and I'm totally ok with that.
At least I know what I like and have found ways to acquire it as physical media, even if it's often a struggle.
So this gives most of us, as a more seriously committed group of "Red Pill" taking music lovers, to recognize when the pop-culture focused, profit-driven industry gets it so right, that even people who generally hate pop-music & culture have to overcome their sometimes prejudicial reluctance to board the "Blue Pill" train and just enjoy the ride for a few minutes.