The measurement of the Hubble constant using delay times between multiple images of lensed supernovae.
The first transit spectrum of an exoplanet atmosphere.
The first directly imaged exoplanet.
(They could hand out Nobel Prizes in the field of exoplanets like candy.)
"conferred the greatest benefit to humankind"
So while those things are cool and groundbreaking, I'd say they have yet to cross the threshold into "greatest benefit to humankind"
Detecting gravitational radiation from the merger of two black holes was an incredible step forward for our understanding of the universe. It will not practically change your life in any way.