It depends on the owner of the build, when the building was built, and how it was made what kind of units they have. When my wife was in college, the apartment she shared had a heat pump unit, that worked for both heat and A/c (a heat pump and an A/C are identical, if reversed, in a/s mode they put the air over the condensor/heat exchanger when the coolant expands, and push the heat outside, in a heat pump they run the blower over the heated output when it is compressed and expel cold air. Individual units like that can be cheaper to install, not to mention that the apartment owner doesn’t have to worry about the central boiler (for heat, they obviously do for hot water), and they don’t have to worry about in a cold winter, the extra bills from centralized heat. A lot of apartment buildings have central heat, though, and the cost is in the rent, it all depends.
For a conversion, wiring a basboard electric heat unit is relatively easy, usually is just a 220 volt line, not a big deal, and again, they don’t have to worry about the effects of a cold winter.
As far as gas heat in the apartment, it depends on how they are heating it. Some places use what is called a hydronic system, they have a hot water gas heater in the apartment, and they run a low pressure line off of it to heat the space (often the heat coils are under the floor). Others will have a small gas unit with forced hot air. In terms of safety, as long as the unit was installed properly, and has proper venting, gas units are not unsafe. It is always wise to have a CO detector, even a gas stove could cause problems, and given how cheap they are, dumb not to have one.
Obviously, some places don’t have natural gas. In the midwest from what I am led to understand and in some other rural areas, propane is used, stored in tanks. Problem with that is in really cold weather, propane can be in short supply, since it is refined from either natural gas or as a byproduct of distilling from oil.
With electric baseboard heat in a house, the one saving grace is you can have a thermostat in each room, and turn off the rooms you aren’t using, which in theory can save you a lot of money, because you use only what you are in. However,even with programmable thermostats, people forget or don’t bother, and it can be very costly, as efficient as electric heat is, its cost factor is order of magnitudes higher that natural gas, on a cost/ btu output basis. I don’t have a conversion figure, natural gas is measured on a cubic foot basis, electricity on Killowatt hours, but in most places electricity will be a lot more expensive .take a look at the estimate cost of gas versus electric dryers, same principle), it is usually gas is 1/2 the cost of electric to 60% of so.
A lot depends on where you live. In some parts of the country, electric power is cheap, in regions like the TVA, electricity is generated by uncle sam, and they can only charge the cost of delivery, which last I checked was about 10c/KWH (same in Washington state, some places in NY State with NY State power authority), and in those areas it might be cost comparable. In most places, with private electric companies, the cost is a lot more, in the NYC region electric is roughly 25c/KWH, and gas is away cheaper, especially since the price of Natural gas has dropped a lot in recent years. For a small apartment, it may not be that much of a difference, though, given it takes a lot less to keep it warm versus a house. I would go with the gas unit myself, no sense in overpaying if you don’t have to, if you otherwise like the gas apartments.