I reckon about half to two-thirds of the current RAF pilot intake have degrees. Rumour control has it that the top brass are looking to reduce this proportion, because they want people to reach the front line aged 21 instead of 24. However, given that Tony apparently wants universal higher education, the pool of suitable non-graduates will surely reduce over the next few years (with the honourable exception, of course, of cadets who are so committed to a flying career that they decide to skip uni). As an aside, it's funny how often policy changes on this matter - six years ago a friend of mine applied to the RAF straight from sixth form and was told to go to uni first (without even being OASC'd)!
As regards your choice of subject, I would say it has absolutely no bearing at all on your career. Specialist knowledge from (e.g.) aerodynamic engineering or avionics degrees is not required - RAF training courses are designed to cater for the lowest common denominator. Some of your future colleagues may not have done maths or physics since GCSE! So go ahead and pick the course that you will enjoy the most...
As for choice of university, that's a different matter, and one that would prompt an eternity of bickering.... so I won't even go there!!