What's a good white paint for customs?

Paint in thin layers. The first layer or two will show brush strokes, but later ones will smooth things out. Just make sure your paints are thinned down and you have a fine haired brush.

Maybe try an airbrush? Maybe thin out the paints?

Theyve all been the same for me. White is more about technique than brand. Currently using Formula P3 white, watered down a little. I also have an old bottle of Testors Flat White that I watered down directly in the bottle, I use that for finer details. They both lay flat and smooth.

For the quickest way for painting it though, I use VHT Vinyl Dye. Its completly smooth and more durable.