Go for propane. Cleaner burning, less pollution. People usually go for diesel if they have red already on site. A bad call anyway, "space" heaters are the worst route to go. Not that I minded going home smelling of burnt diesel, I just got fed-up with coughing-up loads of black muck. My current respiratory ailments are in large part due to working in heavily contaminated workshop air, no small part being due to space heaters:Diesel-fuelled. Still, at least the sulphur content of red is low now!

I concur with JohnMurray and would always opt for natural gas or propane. Diesel is a nasty one to have indoors and should be avoided if possible. There is no statutory duty reason why it cannot be used, in the same way as there is no statutory reason why diesel forklifts cannot be used indoors, but the fumes are unpleasant and propane is a better option.

I would suggest you contact your fire insurers before you get either a diesel or propane heater if they are of the transportable type. Most insurers dislike any form of portable heater where there is the possibility of a naked flame. Some insurers put a warranty on their fire policies stating that such heaters must not be used. In simple terms if you have a fire and one of these types of heaters is on the premises, even if it was not involved in the fire would invalidate your insurance claim. Fixed indirect heating all the time.