I avoid the QF A380s because I have had substantial delays on them – in my opinion, the RR Trent 900 engines on them are unreliable. I don’t think they are unsafe (as per the QF 32 issue out of SIN) but I don’t think you can rely on them to get you anywhere on time.
You could, of course, fly on a number of other QF services via SIN, BKK or HKG that utilise 747-400 aircraft. These are much more reliable, and quite pleasant in F.
Or you could do what I do, and fly BA’s 747-400s. I’m a great fan of the BA jumbos, and if you get the new F, all the better.
A word of caution – if you fly BA or QF LHR-SIN-SYD or LHR-BKK-SYD, you will depart out of Terminal 3 at LHR. and you will not be able to use the wonderful BA Terminal 5 lounges (including the Concorde Room). CX flights also depart from T3.
My preferred routing is LHR-HKG on BA (meaning I depart from T5) and then QF from HKG to Australia. The downside is that the QF flights ex HKG don’t offer F. You could though do LHR-HKG on BA, and then CX for HKG-SYD (which will also allow you to use the great Cathay First lounge in HKG).
In SYD, the QF First lounge is superb. It can be accessed by QF and BA F pax, and oneworld Emerald. Whilst CX does use the QF lounges in SYD, I’m not sure if flying F with CX gets you access to the F lounge, or if access is to the Business lounge.