You do have an opportunity to request where you are stationed. If your unit has more than one airframe, you may also communicate a preference. Please remember, what you end up in. station or airframe has more to do with the needs of the service that day, than anything else.
Still, if there are open slots on either airframe, your Leading Chief will be able to put you where your interests lie.
Keep an open mind. They all have their pluses and minuses.
AMT or AET can be a Flight Mechanic (FM)on helos. Dropmasters (DM) and Loadmasters (LM) are usually AMTs, Avionics Operator, Radio Operator, Navigator usually AET. Some sensor operators are AMTs. Of course AST is the Rescue Swimmer on helos. Flight Engineers have been AMTs, some AETs now.
Then there is the Gunner Positions on the HITRON helos, and on H65s and H60s. That is still evolving. I'll let someone in that world comment.
If you are considering joining, then go see the local Recruiter and he can arrange for one through the OPS department or PAO ofice. You would want to ask to spend time with the Leading Chief or Command Master Chief. Looking in the local phone book for the number and talking directly to either would help in your quest. If calling you will probably need to make an appointment as both of these people are very busy.
Hook up with the ST.Pete recruiter's office, one of the recruiters there was stationed here and he should be able to swing by and give you a tour. If they can't hook you up let me know and we'll arrange something.