Unless you really want to see HKG for the day, I would take the quicker of the two routes (i.e., SQ). There is very little difference between the hard or soft products of the two itineraries you have.

The intra-Asia 777 flights on SQ and CX both have recliner-style seats (CX does fly DPS-HKG with a 744 on certain days of the week; that airplane has lie-flat beds).

The SQ 777-300 to MEL uses their new "regional" seats, which are angled lie-flat contraptions. They aren't the fancy seats you will find on the A380/77W, but I find them more than fine, especially for a relatively short flight like SIN-MEL.

I am assuming you know the CX/QF experience since you posted in the SQ forum, so I will not be redundant and contrast them. All I will say is that SQ/CX/QF are all pretty similar on the equipment you are talking about.