Gas or electric boiler?

This depends on the area/state you are in. Where i am at NY electric would not be an option. In order to use natural gas you would need an utility provider... meaning this would be directly piped to your house. If this is the case then ussually is the cheapest option. If not then propane would be you only other option. One other thing to look into is fuel oil. Remember, you get more btu,s out of 1 gallon of fuel oil then you do naturel gas or propane. Although there is more maintenance to fuel oil and it is expensive. I have a combination of fuels. I have a propane furnace and use an air tight wood stove to suplement my cost.