>>33308591 (OP)For the average person not using an adblocker, both YouTube and Spotify are free with ads, thus equal options. But Spotify is a single-purpose application made for music and so it's more satisfying to sort through libraries and make playlists on there, plus there's no shitty rips or music videos with 2 minutes of fluff before the song like on YouTube. Actually, most people didn't think through it that far, they just were marketed to, tried Spotify, and then kept using it because it works.
If you want to put in more effort to sift through some junk, YouTube is the best option since there is a lot of unreleased, unofficial, remixed, and non-commercial music on there. The highest return is downloading those YouTube-exclusive songs and mixing them with your offline collection of high quality pirated music but I've never bothered with that.