A difficult question to answer because there is no right or wrong answer. One route that may work well for one individual may be disastrous for another so all you can do is solicit as many opinions and experiences as possible and make a decision.
Unless its what you really want to do I would not apply for the R.A.F. There are a lot of very good candidates competing for a small number of places therefore they can pick and choose who they take.
With regards to university there are degrees and there are degrees. Do not go for the easy and fashionable subjects. If its easy then by definition anyone can do it so your obtaining that degree does not really prove anything. A maths/science based degree from a good university will show that you have a high level of numeracy and literacy as well as teach you to think logically. These are all skills that are useful in aviation as well as many other fields. Above all choose a subject that will interest you.
I decided to pursue a well paid career in a job that interests me and use the money that I would have paid for airline training to fly for leisure.