Spray pumps come in a variety of sizes and strengths, but for the home owners, it boils down to using it one or two times and forgetting it in the garage.  I recommend that you rent it from your nearest rental center and the size of the gun only needs to be a Titan 440 or a Graco 450.  The tips to use: If you are wanting a significant amount of paint to apply, like doing an exterior stucco project, use a 517.  Anything bigger and you’ll have an issue with your pump keeping up with the demand.  Spraying indoors, like drywall, use a 417 – and when using it to paint doors and trim, use a 212.