I was in the AF for 8 years. Please do yourself a favor and pick a job BEFORE you go in for your final MEPS appointment.

As far as "mechanic," that's a really broad range of jobs. There's avionics, aircrew life support, crew chief, engine maintenance, general maintenance, etc.

How was your ASVAB score? If it's about a 70, you can do any job you want. I'd suggest something that has the potential for a lot of jobs when you leave the AF. The first one that comes to mind is a network technician. EVERYONE needs people to install/maintain networks. Plus, you'll be able to go to any duty station in the world.

PM me if you have more questions about the AF, I'll be glad to answer them as best as I can.