Which is more efficient and cost less to use

If you're talking electric... then there is not a huge difference. The amount of heat is really dependent on the amount of electricity used. Some boast amazing amounts of heat at a fraction of the cost, but in reality a 100% efficient heater can only put out as much as its given. Some of the older models had as low as 80% heat output, but most are near 100%. Generally speaking, base board heaters will cost you less. They are integrated into the home so that they are more controlled. The thermostats on them are more exact.

Also you figure you get a better convection current. The baseboard heats the cold air which settles on the floor, and it rises to form a constant current around the room. This allows for a more even heating; although the heated side of the room will be noticeably warmer it serves far greater equilibrium than most space heaters.

Also, don't forget the safety factor. If a baseboard heater is professionally installed it has little to no chance of being a fire hazard. Some even come so that they are safe to touch without danger of burns. A space heater that effectively warms a room is often extremely hot on the outside, and sometimes poor design, or even random objects getting lodged in it can cause fires.

If you have a fairly large space heater with a good blower, it will warm a room much quicker than baseboards, however while in operation you will find that it consumes much more energy. If you are looking for a heater to warm the living room a little more while you watch TV, then a space heater is the thing to use. If you are talking about heating a room to a constant temperature then I would suggest baseboard.

If you are not talking about electric, say propane or kerosene, then you are nuts to use a space heater. Those types of heaters are not legal in some states, and often designed for work related environments. It makes sense to use a salamander heater in an auto shop to take the chill off, but not a house. Generally speaking you will find that propane and natural gas puts out plenty more heat for your money than electricity.

Heating oils and other liquid heating fluids are not always as hot as propane, but still more effective and cost efficient than electricity. It may not seem to make sense to use anything other than electric for baseboards, but with a boiler type system, you have limitless options.

Good Luck

If it is a choice between electric baseboard heaters or electric space heaters there really is no difference since electric all heaters all run at 100% efficiency. If economy of operation is of upmost importance then I agree with the infoJunkie4life since usually a high efficiency gas or oil furnace will offer a cheaper fuel source than using electric.