I presume from some of your other posts (and having the choice of A380 and 77W) it will be from LHR. Heading eastbound to SIN where all SQ flights are "overnight", the A380 is almost certainly better.

However, heading back to LHR , if you wife is not a good sleeper, I'd highly recommend taking a day flight, irrespective of whether 77W or A380. You don't feel the need or pressure to sleep (although dozing is of course possible), and you will get to enjoy the F experience fully. Currently there is 9am departure, but I think eventually the flight after noon is coming back as well, and as someone who also doesn't sleep that well on aircraft, I would take either of these over the over-nighters, whatever aircraft you could get.