Avionics or mechanical technician

Hi, I'm looking to join the Air Force after my a-levels and have a meeting booked with a recruiter next week and am undecided between joining as an avionics technician or a mechanical technician and although this will be something I'll discuss in the meeting, I just wanted to get some further knowledge first.

A big part of why I want to join is for the travel prospects. On the RAF website, it has "travelling the world" as a part of the job description for the avionics technician and not the mechanical tech, does anyone know how often you would get opportunities to travel in both avionics and mechanical? I spoke to an avionics technician at RIAT last year who worked on c17s and he said that he commonly travelled to America, but I didn't get the chance to talk to any mechanical engineers.

Another question I have is what are promotional opportunities like in the engineering sector of the air force? I can imagine it's competitive with the amount of engineers there are, however is it well achievable for many?

Also finally I was wondering what career paths out of the air force are like if you were to leave after having done a career in avionics or mechanical engineering. I'm finishing year 13 this year and haven't applied to university as I am strongly set on the air force, however in the back of my mind I do have concerns regarding what I would do if I were in the air force for a while and then left.

Thank you in advance :)