One thing to consider is that singapore are using the A380 out of heathrow to singapore and then the b777 -300er to Auckland.
when we flew with Air nz last year they used the B777 all the way. The stop over in LA was not great as you are kept in a holding room for 2 hrs and cannot use the facilities of the airport.
That said the team on board were awesome!!!! they could not do enough for us and our 3 children 11,9 & 3. At one point the miserable old git that sat behind my wife complained that she kept moving her seat when trying to get our youngest off to sleep (not easy at the best of times but on a long haul flight in economy, need I say more). The lovely hostess wanted to have a quiet word with him but we said that he was not worth it. She then said that they had a couple of spaces in Business class and if Tracy or I wanted to one of us could go and grab a couple of hours sleep upstairs.
It may be worth your while checking out the blurb on the websites. It would be interesting to see if either of them will allow the main visa holder any additional allowance if you are emigrating.
All the best
andrew