Hi 10bob,
If you are looking to boost your miles then BA is probably the way to go.
Of course, I would recommend Virgin Atlantic for your trip. By November most (if not all) of the A340-600s will be fitted with the Upper Class Suite - the biggest flat bed in Business Class.
Also onboard you can select your food from the Freedom menu which allows you to eat what you want, when you want.
A fully flexible Upper Class ticket also includes limo transfers to/from LHR within a certain radius.
As an alternative to BA Exec you could join Virgin Atlantic Flying Club and earn generous mileage for this trip. Miles can be redeemed for Virgin or partner airline flights as well as a variety of leisure activities.
I'm happy to help if you've got any questions about Virgin Atlantic.