Welcome to Flyer Talk
longhaul
Are you in economy or business or first?
If first then SQ's 747 is best (since the 772er has no first).
If business then both have spacebeds, little difference in seat/ife. However 747 has the option of upper deck (which some like) and the risk of middle seat (lower deck config is 2-3-2).
If economy then IIRC 772er has an extra 1-2" pitch (basically more legroom) but otherwise similar. Again, 747 has more risk of middle seat than 772er.