How do you compare propane with other fuels?
Measure how much an equivalent amount of energy costs. 
The most common measuring unit for energy is the British Thermal Unit or Btu. Because a Btu is a relatively small measurement, most comparisons are made based on a fixed number of 100,000 Btus. By knowing your price per gallon and per kilowatt hour, you can compare the cost of these energy sources.
100,000 Btu's =
Heating Oil
1.09 gallons
29.31 kilowatt hours
.72 gallons
  Compare efficiency ratings between fuels.
Electricity is most often considered to be 100% efficient, because none of the energy is given off as exhaust. Propane gas and diesel are both assumed to be about 80% efficient at the consumer's level. However, when efficiencies are evaluated to account for production of the fuel, then electricity falls way below the other two, because so much energy is required to produce the electricity in the first place, and much is lost in transmission lines from electric plant to the consumer's meter. Propane gas is a very efficient fuel source.

Consider the cleanliness of the fuel, which affects maintenance, odors, and environmental concerns.
Propane is a much cleaner fuel than diesel. When burners are properly adjusted, they should not produce soot. Cleaning, maintenance, and wear on parts are less, because of the cleaner system. Diesel exhaust is bad stuff. The exhaust from propane burners is not nearly as potent. Many contractors have switched to using propane-powered heaters on their construction sites, because the diesel-powered units were too overpowering. Many school districts in California are now changing out their diesel buses for propane-powered units in order to keep the environment cleaner for the school children. Cleanliness of the ground and the floor of your home are also considerations. Because propane is a gas, any spill will be dissipated in the air, whereas diesel requires plenty of soap, water and elbow grease and often involves lingering stains and odors. Soil that has been contaminated by diesel from a leaking tank is an even bigger headache.

  Consider the expense of initial purchase of equipment and installation. Propane appliances are often much less expensive than diesel versions. With propane, you have the option to rent a tank rather than the full blown expense to purchase one - and then you don't have to worry about maintaining the tank. When you are dealing with a two story system, diesel fuel requires a pump to move the fuel to the upper floor appliance. Propane is able to be installed anywhere without this added expense and high-maintenance part.