If by "best" we mean a combination of easy availability, lowest cost, reasonable heat output, and fairly clean-burning, then good old denatured alcohol, available by the quart or gallon at Walmart or any paint or hardware store, is undoubtedly the best.
Some people prefer the more expensive "Heet" brand gasline deicer (Yellow bottle). I have tried both and usually go with the cheap stuff. After all, we're not drinking it [hiccup!] :o)