I'd go for the lunchtime departure if available as last time I looked it was operated by a 747 so nicer I think and also the flight is too short for a proper sleep. I need a 9-10 hour flight as by the time you get on board taxi etc and then landing it makes for a nicer sleep. I have made the mistake before on the late flight from LHR to DXB in Club world so slightly different but would always go for the lunchtime flight in the future.