WHo here primes every model prior to paint? If you do, what is your favorite base color primer?
I always prime my models. As far as a favorite color, I have been using a dark gray because that is the only color I have been able to find in an automotive primer. I am going to try experimenting with just using a flat color as a primer, though, to see if I can get some different effects with lighter or darker base coats. I model mainly automotive subjects so the color tints and effects are fairly important to me.
Ray
I always prime in either light or dark grey; just whatever primer I reach first. 
For armor, I use flat black. When I put an uneven topcoat on, I already have a working faded look. As a general rule, however, the determinant factor in primer color will depend on the topcoat you want. For very light or potentially translucent colors, use a light primer; in many cases white is the color of choice. For darker colors, a gray primer is would be better (gray automotive primer, for example).
Gip Winecoff
Well, I’m still not very experienced, but I’ve recently used Testors light aircraft grey spray enamel as a primer for a plane I’m working on. I’m very pleased with the results so far.
Regards,
-Drew