Whenever possible, the tenant should pay. Some buildings have one central boiler/furnace for the heat and hot water and those have to have the heat included.
If someone has to have the utilities included it frequently means they owe the utility company a lot of money and if you rent to them they will soon owe you a lot of money.
People also will be wasteful with utilities they don't pay for. They crank the heat or AC with the windows open and leave it on when they are not there.
My area has a lot of duplexes with heat included and separate electric. On a lot of the ones I manage we have blocked off the vents to one unit and put in electric baseboard heat with individual thermostats for each room so that both units can pay their own heat.