Wi-Fi is better for music since these connections have much higher bandwidth than Bluetooth, meaning your music isn’t additionally compressed, making for higher-quality audio. Bluetooth can still sound good and is very useful (and is probably good enough), but for lossless or hi-res audio, Wi-Fi is your only option.
Bluetooth may not offer the highest-quality audio, but the good news is in many cases, this doesn’t matter much. If you’re doing most of your listening via Spotify, a higher bandwidth connection isn’t going to offer any sort of upgrade anyway (since Spotify doesn’t have the best audio quality).
Some streaming services like Tidal, Deezer, Apple Music, and Amazon Music Unlimited offer either lossless audio, hi-res audio, or both. With these, you may notice a slight upgrade in sound quality over Wi-Fi, but even that is debatable.
See https://www.howtogeek.com/878574/bluetooth-vs-wi-fi-music-which-has-better-audio-quality/