With regards to regimental selection, the air corps is rather unique. The RE are highly sought after but since it isa corps there are a lot of places and hence, arguably, if you are in the top half performance wise and determined enough to join the RE (even better with engineering background) you will probably succeed. The most over subsribed regiments are probably actually the infantry regiments Coldstream, PARA etc and Blues & Royals/ Life Guards within HAC none of which take women. The ONLY frontline roles (officially) within the british army are the select band in the Apache Attack helicopter. To get selected however requires more than just solid performance at RMAS and a good interview. Over and above selection for other regiments/corps you are required to pass aptitude tests and full medical examinationat RAF Cranwell. If successful, you will then go onto do the 3 week flying grading course at Middle Wallop. It is only by doing this that you can then earn yourself a place at the selection interview!!!! Inevitably, whilst the AAC is highly sought after, it isn't particualy competitive at the interview stage since most people have already been weeded out due to medical/aptitude tests or lack of progress during grading. If you are dedicated about flying and want to spend your entire career flying it is important to remember that Front Seat in the AH over Afghan would give some formidale experience but, as an officer, your career is orietated to leadership & managment and you WILL spend desk tours as an adj/ops officer etc. Re ARMY vs RAF, think whether you would be happy in the Army if you didn't get AAC (personally i think there is more variety). If your career ambition is to spend the rest of your days flying perhaps consider the RAF is more appropriate where you effectively sacrifice rank for more flying. Of course, if you want FJ it's a no brainer unless you are the lucky AAC officer with the tour at Empire test pilots school!!!!
Either way, would advocate going along to meet members from each so you can get a 'feel' for the ethos of each arm.