When it comes to painting, the type of primer you use really depends on the surface you're painting. However, for a general-purpose primer that can be used on a variety of surfaces, including wood, metal, and plastic, I would recommend using a high-quality acrylic-based primer. Acrylic-based primers are versatile, fast-drying, and provide good coverage, making them ideal for most painting projects. Some popular options include Zinsser Bulls Eye 1-2-3 and Kilz Original Primer.