The factory bus heaters that operate off the coolant are excellent. Big and clunky, but put out a lot of otherwise wasted heat over the road. As for propane, catalytic heaters are far and away the most efficient.
i used a webasto knock-off called "Planar" diesel fired heat.
the problem i had with the heater is it doesnt burn right over 9000'. when it fires up... it just smokes, a lot of smoke. looks like cheech and chong are camping with white smoke billowing from the exhaust. i think the webastos have the same warning, not for high altitude heating.
for high altitude heat i had to get a heaterbuddy portable.