I always use enamels like MM for cars. I find it easier to get a good gloss with them.
I hesitate to use acrylics in my airbrush. I have had a couple of instances when I was distracted when painting and left the brush go too long without cleaning (I don't mean days, I mean like an hour) and it was hard to clean. I have no problem with using acrylic spray cans.
I do brush acrylics- like the fast drying time.
I always prime under both enamels and acrylics. Testors MM (and even their square bottles) are my default, and I use Tamiya acrylics
I use Floquil Old Silver for a very shiny brush silver/chrome. For airbrush I use Alclad for larger surfaces.