Hydronic may end up more comfortable, but probably isn't any more efficient (assuming you are talking about an oil-filled electric unit rather than a boiler fed unit). Watts are watts. With more mass, the hydronic would take longer to heat up and cool down, so it may cycle on and off less, but would take longer to get hot. Safety-wise, there probably is no big difference, although I suppose it's possible to start a fire with a conventional electric, you'd probably have to try. An oil-filled unit would have a lower maximum temp that probably isn't above the flash point of most materials.