Generally, darker colors and metallics will be harder, because the darker colors show light reflections more, and metallics offer more of a problem than solids for getting the color even.

If you plan on sanding and buffing, medium shades like this will look much better.

If you are not a great bodyman, avoid the dark colors, as they will magnify any flaws in the surface.

If you are a lousy bodyman...are unsure about your talent with a spraygun,... and don't have the patience to sand and buff....use light solid colors.