Have you already gotten your ASVAB score? This will determine your selection of jobs, and then you will (as other answerers have mentioned) select your Top 5. My initial frustration was that the majority of jobs that I wanted (Including Computers, and Technical Applications Specialist) involved taking additional tests. My counselor would NOT let me put those selections on my sheet until I passed the EDPT (Electronic Data Processing Test).
My recruiter really wanted to get me my top choice, however, I felt like the job counselor at MEPS just wanted me to list 5 random jobs and be off.
I was a bit nervous/wary as you are since I had to choose other jobs for my top 5, but I called my recruiter, scheduled the test, and as soon as I got the word that I passed, I spoke to another Air Force counselor and made the change on my job list within the hour.
Once that position was available, my recruiter called me and gave me my leave date (Jan. 19, 2010 Technical Applications Specialist). My job is on my contract, so I'm feeling pretty confident that it will all go through as planned.
Go with your gut- don't just put an Aptitude Area. Then, you won't select an actual job until you are at Basic Training, and like you mentioned, that leaves a lot to chance! Chances are, if you score well on your ASVAB and choose 5 jobs that interest you, you will leave within the next 6 months and have a nice MOS lined up.
One thing that helped me decide was that the counselor let me borrow the book of Job Descriptions over lunch, and I read that along with the list of jobs I qualified for. Some jobs *sound* really cool, and then turn out to be secretarial positions!
Stick to your guns, and work with your recruiter! It sounds like you are trying to be patient- keep it up! I had to wait 6 months, and I know guys that have waited 10 months.
Good luck!