My outside opinion is that Gatwick is Leisure, Heathrow more business. That is unless a leisure destination is so lucrative that it justifies taking up a slot at LHR.
Transfer opportunities have to be considered also. That is flying into LHR purely to transfer onto a long haul flight - considering of course IB flights with this. I would imagine BA have a very good feel as to exactly what long haul flights out of LHR complement their short haul/domestic feeder flights.
Good luck!!