Would it be cheaper to heat with space heaters or the baseboard heaters that are in the apartment?

The window heat pump has the potential to be the most efficient heater you have, but often times uninsulated components and poor sealing will cause more heat loss while not in use than the energy saved over other technologies in use.

The other electric resistive technology heaters will produce 3412 btu's per kwh. Even the watts used by the fans in portable heaters put out the same btu's per watt.

Using a portable heaters does often put stress on electrical circuits that weren't apportioned well for the added load and may cause receptacles, wires, and breakers to wear out prematurely, whereas circuits dedicated for baseboards have a minimum rating of 125% of load.

The baseboard heaters work like the space heaters ON & OFF.  Electric baseboard heating is expensive.  That is just the way it is. Even the oil heater is ELECTRIC.  Dress better indoors. and the heat can be kept lower.  You can't turn off the bathroom heat because water freezes so the toilet tank would crack and the water won't come out the pipes so it has to be at least 40F

The watt setting is not the temperature setting.  If you walk around your place naked, then you want the temperature 70 or 80 or 90.  The wattage just reaches that temperature faster.

/ No they are not on all the time. That is what the thermostat is for.  If you want to live cheaper you put on a sweater and pants all the time.

. You had this problem LAST YEAR.

Sheer money aside, on principle I can't stand the idea of waste, which figures back into the money factor, at least in my mind. If, at worst, one tiny north facing room with a draft and the vent covered is setting the heat so high that the rest of the house is opening all their windows, you are wasting the energy. If the gas bill is $200 that way, in theory you can supplement with an electric space heater and have the overall cost be $50, rather than send $150 literally out the windows. 

The exact details will vary for each place and each person but my 2 cents is setting the central or split baseboard to a fair average and supplementing any heavily lived-in rooms that feel the need. That all said, get a sweater, ya punk! Don't take it too personally, but you can't turn up the heat outside, can you? If you feel the need to be naked inside but are cold and worried about the utility bills, I can see an obvious solution to all these problems.  

Electric is nearly always the most expensive.

BOTH space heaters AND baseboard heaters come in electric AND fuel burning varieties.

A portable baseboard heater IS a space heater.

1 watt of electrical power equals 3.14 BTU's of heat. It makes no difference if the heat comes from a baseboard heater, a stand-alone room heater or an electric central heater. They are all 3.14 btu per watt. Baseboard heaters have no fan as the others do have fans. Therefore the baseboard heater is the most efficient by a hair.

the thermostats control the on/off cycle for the heaters.  from what you say, there are separate thermostats for each room/baseboard heater -- so the space heaters won't be more efficient -- they'll all be just about the same cost if the thermostats are set the same.  -- grampa

     Sounds like your apartment is bigger than you can afford. Look for one that has gas heat and is a better fit for your budget. Or get a roommate to help with this. Grampa B

If you are heating the same space to the same temperature using the same technology, then it will cost the same no matter what shape that technology comes in.

I don't know what a window heat pump is or how much power it uses, but I can tell you that the baseboard heaters, assuming they are the kind with electric coils and not radiators with water in them, will cost the same to run as the plug-in heaters if you are heating the same room to the same temperature. If the baseboard heaters use 3000 watts, they will probably come on less often or for shorter times than a 1500 watt heater that heats the same room.

If there is a thermostat for the baseboard heaters, you can turn it to a lower temperature so the heater comes on less often. In your situation, I would probably shut off the kitchen/bathroom ones, keep the other two at your minimum acceptable temperature when I'm home and awake, and keep the portable heater in the bathroom, always on at a low level. But that's me; I don't know where you most like to be warm.

A certain amount of electricity can only produce a certain amount of heat, and all electric heaters produce almost exactly the same amount of heat per watt.

I have a forced air electric furnace that heats the whole house. Lord knows what wattage it uses, but it needs two whole circuits to itself. One winter I experimented by using two 750-watt oil-filled radiators and only running the furnace for a few weeks at night when it was below freezing outside. From the end of September to the end of April, my heat bill that winter was within $50 of what it was the previous winter using only the forced air furnace. I can get that much variation if we have a slightly cold winter, so basically it costs exactly the same either way.

If all your heat is produced by electricity, then the only ways to reduce the bill are to heat less space, or to use less heat in the spaces you do heat. If you keep one room warm and one room cooler, then you have to close the door to the cooler room or the heat from the warmer room will go there. By all means, turn off all the heat when you go out. You aren't likely to get frozen pipes in an apartment, though it can happen in very old buildings in very cold weather.

Back when I had a wood stove as my main source of heat I would, naturally, come home to a very cold house in winter. I'd just leave my outdoor clothes on until the house warmed up a bit and I had a nice hot cup of tea in me. I had baseboard heaters in every room. The only one I used in the 13 years I lived there was the one in the bathroom. That was the only room I wanted to be really warm. I kept its door closed most of the time so it was always warm. They say most people sleep best in a warm bed in a cool room. An electric blanket, or better yet a heated mattress pad, would be a lot cheaper to run than a heater in the bedroom. Turn it on half an hour or an hour before you go to bed, turn it off when you go to bed, and you ought to be quite comfy at night for a lot less money.

All heating is expensive but especially electric  - the trick is to reduce the need for it. Spend up on draught proofing and insulation as a priority first. Insulated curtains in the bedroom, or even shutters. Put a time switch on appliances if you are worried you might leave them on all night (except things like electric blankets). Check temperatures when using thermostats, often they are unreliable.

Several different A/C maintenance guys have told me that space heaters are the most expensive way to heat a home.  They do not recommend them.  Also, in an apartment building, in most of those buildings, space heaters are illegal, because they are fire hazards.