My boyfriend is going to be joining the military, but he doesn't know which branch to join. We are going to talk to the recruiter tomorrow, but I'd like to know some opinions about the Coast Guard, Air Force and Army. Those are the three he has limited it down to.

I was in the Navy but out of the three you listed I would probably join the Air Force, then the Coast Guard. But, if he wants combat experience the Army would be the best choice.
Also, depends if he is considering a career in the military or just a few years. Does he want to phase into a related civilian occupation in a few years? If that is his goal, he should see which recruiter can guarantee the best options.
Regardless of his motivations or choice of which service, I salute his desire to serve his country.

I say the marines... my man was in the marine core, made a GREAT man out of him!!

He wants to do avionics stuff, and not do much combat stuff. Any other things you know about these branches? Like benefts etc?

My advice, visit all 4 branches and get information from all four branches.

Is he looking at a career ? Or just a job with some training.

Personally I was a air force man myself.