It provides it's own pressure and doesn't have to be pumped. It vaporizes into a gas at normal temperatures. It is stored in liquid form which means that a small tank can hold a lot of fuel. It is cheap and available almost everywhere. Other compressed gasses are more expensive and the tanks don't hold as much.
Propane is probably the ideal fuel for an experimental engine.
Other fuels will work. Anything that can be mixed with air and will provide enough BTUs when burned can be used as a fuel. Gas turbine engines have been run on everything from Hydrogen gas to coal dust. Most commercially built engines are designed to run on kerosene, AKA jet fuel. Diesel fuel and alcohol are also popular fuels.