Would second the positive reports on QF J. From my experiences the service quality on QF J was on a par with BA F especially food and drink quality. I found the cabin crew to be more friendly and refer by name. On the outbound trip I had a malfunctioning seat (upper deck) so got an upgrade to F onboard after the meal service.

The incline of the seat was a bit distracting but I managed almost 9 hours sleep from BKK to LHR. I will be taking CX in J very soon so will be abale o run the 3 way comparison. My money though would be on QF over BA in J all things being equal (and QF consolidated fares are often lower than BA too ex LON).