Thank you all very much for your valuable feedback!

I almost never fly in J, so actually it would be nice to try the Finnair seat for the inbound journey, but for such a long flight I am afraid that I really need food (QR) and not just food-samples (AY).

AY does beat QR in arrival time and arrival airport.
QR (14.55) beats AY (11.20, more traffic jam to BRU) in dep time ex-BRU.
Both AY and QR have 19h travel time: 16h flights + 3h transit. Of course AY has a short BRU-HEL flight (in Y seat, without IFE) and a longer flight HEL-HND, while QR has longer 2 flights with business class seats.

NRT can be a pain, but immigration lines are no problem (resident) and I guess rush hour would be more on trains leaving Tokyo... It is still a later arrival and more distant though, in case of NRT.

Can anyone confirm that a window seat selection is included in the AY business award tickets?
If window seat is extra cost on AY, than I go for QR without further ado.
I not, than I can continue being torn...

Many thanks again!