Really there is no question what you should do.
try for the RAF (or RN), even as an engineer you will always have a chance to fly and the flying is out of this world no matter what aircraft you end up flying (low level, Night Vision Goggles, mainly VFR ops).
Airlines are great but hardly the most interesting flying
I should know I have done both, 12 years in the RN then the last 6 years in the airlines. Do you really want to do the same job for the next 40 years???
As for MIKECR's comment about employers not caring where you come from I'm afraid I have to rubbish the claim that coming from the forces makes no difference, all the ex RAF/RN/Army aircrew who want to fly will get a job within weeks or at worst months after leaving and nyone else from the forces will also be employed quickly, I have flown with Submariners, engineers, chefs, tank drivers and many other ex-military types. employers like the self discipline evident in most service leavers.
But remember the choice is yours.