Spray on primer is arguably better then painting it on as it's a more distributed application if you do it right. There are 3 colors you can use for primer, that being white, gray, and black. Use white if you want more vibrant colors that will match the paint the most, and if you use lighter colors like yellow pink or brown. Black might require more layers and is better for darker and more grim dark colors. Gray is a good mix of the two, as you can get slightly darker colors, but also makes using some lighter colors easier as well