Hands down Tidal. The difference is quality of the tracks is not subtle - it's downright obvious. On my main system (220SE with CM9S2) or on my macbook speakers. There is no contest, no ambiguity - Tidal sound better. And I'm a paying member of Spotiy Premium and Tidal Premium (not even Tidal HiFi).
Tidal vs. Spotify
Tidal sounds better for sure. Search functions aren't as good as Spotify but if you are currently using Spotify, give Tidal a try and let me know what you think!