As has been mentioned earlier, AFCO should be able to arrange for a look at the various training establishments - there's no substitute for talking to the people involved to get a balanced picture.
One of the main concerns with ATC has been that it didn't, necessarily, allow you to take your skills and experience/qualifications into a career in civ control. That is being addressed (albeit only to a limited extent) by the introduction of an 'ESARR5' compliant course. In essence, parts of the JATCC will count towards any future civ training.
Concur with observations on the Flt Ops specialisation (don't do it
!)
Historically, the best prospects whilst in and for taking outside, were to be found in Admin and Supply.
There's a lot of other specialisations that we haven't touched on - use a visit to a Unit to ask loads of questions after doing some research on-line.
Good luck...