They each do different things well.
Spotify IS better at music discovery and making suggestions of other artists you're likely to be interested in. I particularly liked the regular emails giving a list of albums to check out. I tended to like most of them, so their version of a scrobbler is pretty good. As I use Tidal now, I also use the app "Discovr", which is a fun visual spidergram way of learning new artists. I also tend to learn new artists on YouTube channels like NPR Music (one of my favourites) and Sofar Sounds, and then look them up on Tidal. (Check out "Mariachi Flor De Toloache" on NPR Music - such fun!)
But I do prefer the layout of Tidal. I find it has a nicer simpler interface that's really easy and clear to use. Spotify's app seems a little busy in comparison. I also really like the way it stores your own albums, artists and playlists. And since I joined Tidal its catalogue seems to be plugging many gaps it had about a year ago - the special edition extended album of Interstellar for example was missing initially, but is now there in all its glory. Now there are much fewer albums and artists missing, although I would imagine Spotify still just has the edge there.
I do find Tidal a little buggy at times, but I'm willing to overlook its deficiencies for the really beautiful sound quality. I personally find it better than my CD player, because although there's no reason for the files themselves to be superior, my CD player, especially during quiet passages in music, would remind me of its presence by the constant whirr of the disc spinning. Tidal is just silent blackness which seems to add even more contrast to its sound quality.
One downside of Tidal (for me), is the prevalence of rap on its home page since Mr. Z's involvement. I'm into most genres of music, but not rap. Having said that some of their suggested playlists have been excellent. The Herbie Hancock playlist they had a few months ago was superb.
When I had Spotify I used to dart all over the place hopping from one artist to another, but with Tidal I tend to sit and enjoy the albums start to finish more.