Keep in mind that primer is not a basecoat. People often disregard this point, but the primer is designed to allow paint to stick to plastic, so its colours are actually a little duller. To get a high quality model you need to paint over your base coat even if you are painting white over white, or black over black. As a primer, the white and black primer are both fine so long as they aren't too old (I had an old can of black which came out in clumps, I had to strip the model and start again).