If they are P rated tires, generally you fill them according to the door sticker for day to day driving. When you tow, put more air in them. Its makes a world of difference towing. I've been running mine at 40psi in the back.
Keep in mind that tires are made to fit a variety of applications. The tire manufacturer has no idea what the handling characteristics of the vehicle are. The vehicle manufacturer does. Unless you deviate from the OEM specs on tire size, follow the door PSI recommendations for day to day driving.