I wont add too much because Flystar seems to have summed it all up nicely.
But if you intend on making a career out of the industry may I recommend BA over QF for the very simple reason that even if you decide you dont enjoy the flying, at least there is a huge number of opportunity's within the company itself be it cabin crew management or elsewhere. Also like Flystar said, if LHR is really what you want in the long run then you at least have the chance to put your name on a list regardless of how long it may take.