Latex: Aka acrylic or water-based paint (water is the solvent), it's the most DIY-friendly choice because it cleans up with soap and water. Most paint sold today is latex, and in many areas it's the only option available in gallons as more states limit the sale of solvent-based products.
Oil: Known as solvent-based or alkyd paint (mineral spirits are the solvent), it dries slowly and requires paint thinner to clean. But that slow drying time helps oil paint level out, ridding the surface of brush strokes or roller stipples. Oils harden to a durable, enamel shell.
Low-VOC: Paint solvents contain volatile organic compounds that off-gas (creating that paint smell), a health hazard. Recently paint companies have reduced or removed solvents to make healthier products, which are thicker (aka "premium") and dry very quickly. Adding conditioners such as Floetrol or Okon can extend working time without introducing VOCs.
Metal: These paints are formulated to adhere to metal and inhibit rust. Acrylic metal paints are fine for nonferrous metal (such as aluminum), but ferrous metal (like a cast-iron radiator) requires an oil-based metal paint.