I would use untreated and stain/seal myself. Untreated lumber is dried and usually straighter because of this. Pressure, Green, MCA, ACQ Treated is still wet when the manufacturing process is over. It does not go into a kiln unless a certain moisture content is needed. if you can find Fire Treated lumber, that is baiscally green treated lumber a too. Fire Treated lumber has a .25 retention which is basically rot resistant and it is dry.