I like Rusto "Wet Sandable" primer (don't recall what else it's called, maybe the 2x, been awhile since I looked at a can) because it's a high build primer and I can "damp sand" (wet sanding but blotting the wet sandpaper on a towel to limit water on the rocket) and get glass-smooth finishes that take and hold paint well-- no color sanding required.
For color coats, I use a little bit of everything. On scale and semi-scale rockets that use a black and white color scheme, I like the WalMart Colorplace 99 cent a can stuff... it actually does a TERRIFIC job in those applications *if* you've prepared the surface well with the wet sandable primer (ie if you can see an imperfection in the primer finish, you'll see it in the color coat; that's true of ALL color coats though).
For other colors beside the VERY basic selection of WM Colorplace, I usually use Rusto or Duplicolor, or even some of the ag paints from Tractor Supply or other farm stores. The auto supply paints are also very good.
I picked up an external mix airbrush cheap at TSC, and an internal mix single action on closeout at HL and intend to give them a try sooner or later.
The main thing to AVOID LIKE THE PLAGUE is the "primer and paint in one" crap... it TOTALLY misses the point of the primer coat-- which is to fill the imperfections and prepare as perfect a surface as possible for paint. You can't DO that putting the "primer and paint in one" because an ESSENTIAL step in surface prep is sanding out the primer. I start with about 2-3 coats of primer, and sand it down with 220, then switch to 440 grit wet/dry paper, dry sand it, then get a bowl of water and dip the paper in it, blot it on a towel, and "damp sand" it with the damp paper. You'd be amazed at how nicely it smooths out the surface. If you REALLY want it smooth, switch to 600 and damp sand it-- you can LITERALLY get it mirror-finish with primer. I hold it up to the light glint from a window across the house, and look at the reflection of the light (the glint) off the side of the rocket, turning it slowly and inspecting it. If you can see any imperfections in the sanded out primer, you'll see it in the final color coat. Fix the problem right then, get a good smooth imperfection-free finish with the primer, and DON'T SCREW UP PUTTING ON THE COLOR COAT (ie no drips or runs or orange peel) and color sanding is TOTALLY unnecessary-- the finish will be perfect.
Now, some guys will say, "What about tooth?? If the primer is TOO smooth it won't hold onto the color coat, and it'll turn loose or peel over time." I can honestly say I've never had that happen... I've got rockets finished that way over 10 years old and they are still looking great. The primer, even if it *looks* glossy, still has enough "tooth" in that it's permeable (microscopic pores, which is why cars running around in a primer coat will rust under the primer-- the color coat "seals it off" and when it hasn't been painted with a color coat yet, the moisture can go straight through the primer to the metal beneath... and no, damp sanding doesn't hurt the rocket-- it's not enough water or enough time to damage anything-- just sand lightly let the paper do the work; as the sandpaper shaves down the primer the liberated primer particles grab the water and turn into "sanding mud" on the surface of the tube and fins-- periodically wipe it off with a damp paper towel, then dry it with a dry paper towel, dip the paper in water and rub your finger across it until all the particles come loose, blot the sandpaper off on a towel, and go again... the "sanding mud" will get thicker and thicker as you work, as water evaporates and more and more particles sanded off will 'suck up' the moisture... Anyway, the paint can still "grip" the smooth primer enough to stay... in my experience anyway.
Works for me!
Later! OL J R