It depends on what is being painted. For the majority of surfaces, an acrylic is going to last longer. Acrylics are softer, more flexible, and more resistant to chalking. This is because the acrylics have a much higher elasticity rate, so that when the surface, such as timber, expands and contracts with the weather, the paint moves without cracking. Luxury Water Based Acrylic is suitable for areas such as sash windows or any other situation where two surfaces are touching. This is because the general exterior acrylics, being softer, have the tendency to stick to themselves in hot weather, so using this Luxury product will avoid sticking. Oil based primers etc. are necessary for any ferrous metal, such as steel.