If I never camped below freezing BUTANE.. Since it occasionally gets down below freeZing where I hang out .. Propane.
WHY
Propane the vapor temp is right close to -40 (No sure exactly but within 2 degrees) -40 I'm seriously not going to be using the RV.
Butane I think it's 32.. So if the tank gets down to 30.. NO HEAT.
Many have bought propane in the deep south or so they thought, but the dealer filled the tank with Butane, which is cheaper, and pocketed the additional profit. Then they went north and no heat.