Joe,
Yours is a question that I have been asked many times. The simple fact is that it makes more sense for the RAF to get you early – greater return of service and you are more accommodating of the demands of training, more malleable even. For a long time the RAF courted graduates which I suspect owed more to a misguided perception of who should populate the officer cadre – I am glad to see that notion has diminished.
Interestingly, my own circumstances were not too different from yours. I saw university as a stepping-stone to the RAF and applied for a cadetship to study aeronautical engineering– when I was offered Direct Entry I jumped at the chance. Personally, I lucked in – had I waited I would have hit a massive holding crisis that was just over the horizon, taken years to get through and missed out on some amazing experiences.
Therefore, I avoid giving direct advice but encourage anyone in your position to see what each option really represents:
Direct Entry will be fantastic at your current age and you will have a chance to get on with doing something that, from the sound of it, is in your blood. Forget any nonsense about being better placed to achieve high rank – if that alone is what motivates you, become a politician (because you will always be subordinate to one in the RAF).
University will also be an amazing experience, leaving you with a respected qualification, exposure to a broader spectrum of life – and, as correctly observed by the Alligator, lots of girls! The RAF does not care what degree you get. So: A. Choose something really difficult that impinges upon your chances to make the most of all the ancillary opportunities, quickly becomes obsolete and will never be used again if Plan A is successful. Or B, choose something that will be fun, not too difficult, give you a general education that will always be useful and, preferably, have a high ratio of girls attending.
I would not want to turn the clock back and can no more hope to predict what the future holds but, if I were in your position, I would go to university and read history. Or underwater basket weaving!
Then become a fighter pilot.