Hi,
As Genghis the Engineer says, depends what you want to do with your degree --- as HWD says, Maths/Engineering/Physics will get you most places, but are also among the tougher degrees on offer.
As an example though, I work in the Marketing group of a large aviation company and would say that around 80-90% of employees in the team have physics/engineering backgrounds.
Jut thought though - how old are you? If you already have some experience, there are aviation-related Master's courses out there in which you can enrol on without gaining a previous degree - e.g. the MSc Air Transport Management at Cranfield Uni (1-yr full time). You'd enjoy that a lot, but then is very highly aviation specifc for obvious reasons...
Good luck!
Jason