Propane, nice solid flame, easy to adjust, etc. It's very convenient. Natural gas, you can run a small still on your kitchen stove. However, I DO NOT RECOMMEND THIS. (Sry, really wanted that to stand out.) Of all the places to have a catastrophic failure, you don't want one in your kitchen. Any fuel source will work, the bigger point being temperature control. A camp fire works, just feed it slow. Ideally, you'll have a temp gauge on your still.