QFA380 First is very good but I would not agree that Food ad Wine are better on QF than BA. Given the uncertain nature of the BA first product the A380 may be a better option for you as the product will then be consistent.
Crew on QF are not a patch on BA on a good day.
Finally there are continuing issues with reliability on the A380.
Sydney First Lounge super but you get that no matter who you fly with.
Given the journey why not go A380 LHR SIN and BA SIN SYD to compare… A F ticket on the JSA should be fully interchangeable.