Are you referring to the quality of music i.e. vinyl vs. digital (please don't start that debate again) or quality of music with regards to the artist?
If technology then only a DBT will convince me a technology is supposedly better and most expensive audiophile grade products lose that battle.
If its artists then define quality! And who gets to decide on what is quality music?
I listened to a lot of Metallica, Black Sabbath, etc. when growing up... now very rarely but my cousins and nephews still enjoy them.
I never had a thing for classical music and still don't get what Opera is all about (though I have a few albums from Andrea Bocelli & Luciano Pavarotti).
I hate Lady Gaga but she has fans pretty much all over the world. Ditto for all girl and boy bands.
If numbers (sales) should decide then The Beatles are the best... but many I know many friends don't even like them. I listen to them but they are not my No. 1 band.
I don't even agree with the number one movie on IMDB... The Shawshank Redemption! Movies like The Godfather and even The Dark Knight are way better according to me.