English Ruling

Today at work I was pulled off to the side and asked the question, “Which should be used in this email "a" or "an" before an acronym such as NTF. NTF at work means No Trouble Found.
I answered but now I don't know. This is such a conundrum...

Sentence Examples:
1. Contact (a or an) NSA agent.
2. I flew (a or an) F14.
3. This was (a or an) OOBF[out of box failure].
4. I own (a or an) PS3.
...and then we have NASA. Those acronym's we say as a word.
5. I talked to (a or an) NASA representative.

My initial thought is
a NSA agent
a F14
an OOBF
a PS3
a NASA

but is sounds better as
an NSA agent
an F14
an OOBF
a PS3
a NASA


If anyone has a good ruling please comment.