So honestly, these look to both be great TV's. I don't think you'd necessarily go wrong with either.
That said, I'm a Z9F owner and very, very happy. Some things that swayed me were the Dolby Vision support (as I have access to a lot of DV content via Netflix and AppleTV movies), the fewer reports of DSE (the Q90R doesn't seem too bad with this either, but I've seen a few more reports of it than with the Sony, and some Samsung models are notorious for it), the excellent motion handling, and the reputation for lots of detail in dark scenes (which again, doesn't seem to be too much of an issue with the Q90R, but previous Samsung's tended to crush blacks quite a lot).
One thing to be aware of is, due to the X-Wide Angle layer on the Z9F, reflection handling can be downright WEIRD. Be aware of this in a light-filled room. That said, since the Q90R uses similar technology, it could be the same there - I unfortunately can't tell you that. Either should be plenty bright; I am in shock of how bright the Z9F can get!
Good luck with your decision!