don't worry about the training, the RN has some of the best facilities and instructors in the world, for whatever trade or job you choose, so you will have the best chance to get through it and do well.
My day as an Aircraft engineer is on one of the other newbie's pages so just fish a little and you'll soon find it.
Basically you need to find something that suits you in your intellegence and interests, or it's going to be a long 4 years to get out. Don't be co-erced into choosing a job, just because it's what the Navy really need at the moment. Not saying it still happens, but it used to, and nearly did to me. If you're bright enough, you should perhaps be thinking about Engineering or Medical branches because you'll maybe find them more of a challenge and will be better accredited for the transition back into a civvy. If in doubt -ask, what will this benefit me for Civvy life? What will this enable me to do after i leave the Navy? If they can't find the answers, or you're not happy with them, bin it and choose something that you are happy with.
As an alternative, join a branch that you like the sound of, and if you want quals for Civvy life, go to night school or the Open Uni or something. Lots of Matelots do, and the RN will help with the cost.
Hpoe this helps. GB