IMHO they are both great services, and I do not find any SQ difference between them.
As it has been already mentioned, they serve a slightly different public.
If you’re into Hip Hop et similia, you’ll see that TIDAL is very aimed at those tastes. But you can find pretty much anything on it, and they’re starting to offer master quality materials as well.
I ABSOLUTELY love the editorial line of QOBUZ: their selection of playlists, albums and curated contents is second to none.