a propane heater should have no smell. The heaters that mount to the tank are radiant heaters, they work fine, but they get very hot and will burn anything they touch. I don't think they're very useful as a home garage heater, because of the required clearances, and straight line heating. I use a forced air heater. I had a 30K btu one for years, which is enough to heat a normal garage. I replaced it with a 60K btu one that turns down to 30k btiu, because I wanted to be able to heat the space up faster. It (and all its ilk) are loud, both from the fan and the burner. not a big deal to me, but some people hate it. It'll run 6 hours or so on a 20lb tank on high, but if it's cold it won't be able to do that because the tank freezes. I use a 40lb tank, which reduces the freeze factor and is more convenient to deal with filling. Tank freezing is probably not much of a problem in NC, though.
For a rough estimate on run time, figure propane at 20k btu/lb. Also remember that exchange grill tanks are only filled with 15lbs, because they're a scam targeting people too lazy to do work. Find someone who fills the tank and charges per gallon, much cheaper and you get a full tank (and you don't give the exchange people propane if you refill early. See "they're a scam"...).