Personally, I would always recommend not flying on Christmas day as your fellow passengers are often miserable!!! LOL!!! Only joking!!!
If Cathay or the BA/QF flights are your only options then I would say that Cathay have the best product down the back. Qantas I generally avoid when I can and well, I work for BA so as much as I love them I still need to be objective!!! If its Business your travelling in then I would recommend BA as I still think they have the best seat and by next xmas your flight may even have the new Club World seat!!!
HOWEVER....If other airlines were to pop into the equation....I would avoid emirates (minute seats and dropping standards all the time) but I would seriously consider SIA!!!