Natural gas is the only way to go. Diesel will only get you so far before it has to be refueled. Natty will run cleaner and you won't have to worry about how much fuel you have on hand. You will pay a little more for a natty gen set than a diesel. Olympian makes a nice product. Buy bigger than you need and have a automated switching system with a constant power supply so there is NO interuption in service during the transition.