SQ for sure. (Given that the other choices to Aus from Europe are TG or OS).

You could also consider flying new C class on LH metal till SIN and then connect to SQ.

P.S.: Ensure you check carefully which SQ flights you take from SIN-Australia. IIRC all the SYD flights have spacebeds, but only one of the MEL flights does. If you choose a 744 operated flight you'll always be safe though!