The heaters designed for workshops that use the waste oil from your local car or truck garage are the biz, steady heat and relatively free from fumes smells etc, downside they are a high initial cost but if you can source the oil for nothing then payback is quick.

I've had far too many diesel space heaters that you end up smelling and exhaling breath that smells of oil fumes, doesn't half kill the old passion sessions with the better half, straight off.

The LPG Green House heaters which are thermostatically controlled, if your workshop is large, are really good, downside is they do end up putting large amounts of condensation into your workshop which is not great for epoxy.

The best workshop heater I've had was a wood burner, get a good quality one and you can shut them down enough that they will still light the next day, you don't need a very big unit either as they are better to be run at mid heat than to control them down to far where they fume and "oil" up the flues from lack of heat.