Also, QF does not fly BNE - BKK direct, so you would have to always go via SIN and then 3K up from there.
Or backtrack via SYD to get the SYD - BKK flight.
TG does not fly to BNE.
JohnK goes to BKK often, and he is BNE based.
Probably as mentioned above, SQ would be the one to go for.
They still have a liaison with VAd, but their tie in flights on the dom sector agreement, can be a bit iffy, ie, if you put in your SQ KF # into a VA booking, if its not a codeshare, ie, pure Aust dom flight, SQ might decline the points.
So, keep VA alive as well, and if you occasionally shop at Coles, or 7 eleven, you can keep your VA points alive and not expire, as long as there is activity per 24 months.
KF points do expire 3 years after accumulation, (no extensions possible), so after you have amassed the points in KF, move the points to VA so you can use the points on Aust VAd flights.
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Both systems (QF and SQ) do need you to fly a lot to climb the status ladder.
If you are going to be flying J (business) I would go with SQ, go with them, SIN Changi is a great airport to transit, it also has the internal hotel, or the Holiday Inn next to the airport to rest overnight, or have some downtime between flights.
I think SQ has 3 flights a day from BNE - SIN, QF has 1.
To get to QF SG, you need 700 SC, and that is a lot.
You don't say what class you are flying, or if your employer/payer pays for the flight.
If with J (business), SQ would be my first choice, if I were doing the flying.
QFd would be good for Aust dom flights, with QFd flights, if there are U seats, you can upgrade immediately.
On QFi, flights, if you are QF NB, your upgrade chances are down the bottom.
On my several SQ flights, I can't fault the high standards of the SQ inflight crew.
They really work hard.
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Also as of now, QF is using AY planes and crew, from SYD - BKK, not sure for how long, on these flights, there are premY offerings, so for the time being, if you want to fly SYD - BKK for a bit less than paying J, and collecting QFF points and QFF SC, it might be of to fly with QF's AY service.
But that is up to you to decide, as to if its financially worth it.
Maybe in 12 months, QF might again bring their own planes back to SYD - BKK, and they don't have premY.