For smoking what and at what temps and for how long?
Me? Charcoal UDS for smoking meats (butts, ribs, brisket, etc). A load of charcoal will burn 12 hours at 225* temps. That is set it and forget it simple and the outcome is always good.
Propane drum for all manner of smoked sausage. Low, consistent temps for hour after hour after hour.
Never tried electric, but for small batches, the commercial units should work the same way. If it has a thermostat that gives reliable temperature control, this is probably the best option.
For most of us, fuel cost is not a consideration, but for grins, it would be nice for someone to calculate the energy/fuel cost of electric vs propane for a typical smoke.