The type of gun depends on the paint. Each manufacturer will recommend a specific size fluid needle and air cap for their paint. They also specify a certain line pressure at the gun's inlet regulator. So get the paint first and then get the gun.
You may be able to get an all purpose gun but you'll need different fluid needles to go with it so that you can use different paints. You also have to be able to mix the paint at the recommended viscosity and there's different ways of doing that.