Do you plan to fly QF again in the future?
QF PS will give each of you one visit to a QF lounge, not including this upcoming one, as you would each have entry to the QF J lounge in SYD, not as flash bang as the QF F lounge in Sydney, but still good.
I still have a soft spot for QF, so would stick with them.
But to each, their own.
If Alaskan Airlines would be flown again, then it would be of benefit to you in future, ie, you are going to fly with a OW airline again, then it would ok to go that way, I suppose.
LA as in LATAM is also not linked to (Air) NZ, so you can't park SC with (Air) NZ.
BUT, if you don't plan to fly QF or OW again, then just collect SC in QF and then let that drop after your 2nd QF flight, after this one.
BNE QP is not that bad, would be one of the better ones post refreshment being done to it.
I am probably going to fall to QF PS later in 2018, but I will still keep my SC in both nests, QF and VA, as I don't fly far out internationally.
I flew with them (LATAM) in J from SYD as far as AKL, and it was great being able to look out the window and not strain my neck, as the windows were indeed wide.
If you and the wife like window views, maybe pick seats one behind the other.
PS, even though the QF and LATAM blurb says seating not guaranteed, my seat choice made in QF's booking did carry across to the LATAM system.
Edit: as you are coming in from BNE as a linkek ticket via SYD, the following has been amended by me.
Ask for Express Path in BNE for SYD, which was in operation, had gotten card from LATAM check in girl.
BNE dom check in might say collect it in SYD.
Outgoing immi was easy, Smartgate easy to use, and no more OPC which is a blessing.
The walk from the SYDi QF J lounge is quite far to where the gate that LATAM departs from, so give it a bit of time prior to 11am to get out to the gate, mine was gate 34/36.
QFi J lounge is near gate 10.
LATAM crew were good, and "not as chummy and pally, or chatty" as the EK crew I got when I flew EK F back to MEL.
Nice not having a herring bone on the 787. Don't like that choice of seating.
Edit: ah, I see, flying in from BNE, hopefully your first flight from BNE will be arrive early enough to do a transfer by the QF bus from T3 to T1.
Have done that one too in the past.
As you both live in BNE, and you will get to feel BNE QP/J lounge, maybe save the PS lounge invite for MEL/SYD/PER.