I realize you asked for other recommendations, but I suspect you don’t want to actually maintain your own music library but rather want streaming services recommended?
Of the two alternatives you are currently looking for I do have experience with Deezer, although it has been two years at least. The music library is almost as complete as Spotify in my experience I rarely had issues with songs not being on there. The recommendation algorithm at the time was nice, but would sometimes get stuck in a hyper specific genre that would only reinforce itself.
For HIFI audio you basically do need fairly good audio gear for it (decent wired headphones for example), I’d say that for most people it is not worth paying extra for as it is really difficult to tell the difference.
One other service I have used is Youtube Music as it is included in premium. It does not have an HIFI option but otherwise is fairly okay. Basically worth looking into if you were also considering Youtube premium, but otherwise not really special.