crb
Both career paths require hard work and dedication just to get in so research well-this forum will be a good start.
Unfortunately I couldn't say which one would be best for you, but, having had a military flying career and a NATS ATCO job under my considerable belt then I will give you my thoughts on the two.
RN-you will be expected to be a naval officer first and an ATCO second. Expect lots of sea time initially with more land posts coming as you progress in your career. Pay good but as with most military jobs not comparable to the civilian sector. Training and professionalism excellent. The navy will give you the tools to be a well rounded person while giving you exciting challenges and the possibilities of travel.
NATS-Many people join just to control aircraft but the potential for broadening jobs are widespread. Chances are you will stay at your first posting for a considerable period of time but chances to move do exist. Pay and pension excellent (although there is some dissent in the company regarding "banding"). Training and proffessionalism excellent. NATS will also challenge you and the various travel schemes can be quite cheap.
If I was to give you advice I would say apply for both (in case one doesn't work out) but for a young person the military will stand you in great stead for any future career.
Good luck. If you have more specific questions then let me know
