I was booked on QF for NRT-SYD about this time last year and I changed it to try to JL. I think I wrote a quick comparison afterwards. You may want to do a quick search on the QF forum.

As mentioned, seats are pretty much the same. JL's service is a lot better, QF is probably slightly better on the food front. JL has a better dinner, QF has a better/bigger breakfast. QF has better amenities. QF will probably give you jammies for an overnight flight, JL won't give you that.