I'm slapping in for AW, the main reason being that I want to go to sea. I'm led to believe the chances of doing this in the other branches are slim. Coming from a Warfare Branch background (as a rating), I reckon I'll have a slight head start when it comes to things like Ops room stuff, which AW officers do in the ship to shore role.
The part of the job which appeals to me the most though, is acting as a SNO onboard RFAs and civvy ships. My last RN draft was on RFAs so I have a bit of experience working in that sort of mixed environment and also with booties in the force protection role.
Also as an ex dabber I basically did everything the Sea (Res) lads currently do. If deployed as a SNO, leading a team of Sea (Res) lads who are doing a force protection would be a fairly natural progression for me. Given the fact that I know their job inside out, I like to think I'd be reasonably good at understanding their needs and managing them.
Look at where your own skills lie and think about where you might fit in best, if you work as a logistics manager, chances are you'd probably be fairly comfortable in the logistics branch for instance. Of course some people join the reserves to do something completely different from their civvy career, but do consider the difficulties of learning an entirely new job from scratch. You might as well give yourself a head start by doing something you know you have a better chance of being good at.
Just my two cents.
Good luck.