Biggest hit vs. best song
The one that brings this to my mind is Sammy Davis, Jr.'s "Candy Man," which was boffo!. But surely "In the Shelter of Your Arms" was a better song, and a much better performance.
Your candidates?
(We can skip ABBA's "Dancing Queen" — unless I'm unaware of a better song from them: That seems to be a darned near perfect pop song!)