The 772 on BNE runs, has the oldest SQ fully flat business class seats, which are quite wide (some say too wide, but never a problem for me) , and some find uncomfortable, particularly for sitting in (although careful placement of the two cushions that are provided always helps to improve comfort). The A350 seat is much newer, so looks fresh and new, but is narrower and a little more cramped so gets complaints from taller and wide shouldered people. But either is OK. Choose the time that suits you best.
And, the business class on 772 is a lot better than PE on 350. The absence of someone reclining in your face, and all aisle access is a huge plus.