I would recommend looking at a heat pump system. They provide airconditioning in the summer and heat in the winter. You should be able to get more rent with an airconditioned unit.
If the ducts are already there, the cost may be quite tractable. Further, many areas provide tax and utility breaks. For example a direct rebate on a hefty percentage of the capital cost as a direct tax credit or a tax write off.
Since it might be catagorized as a repair the whole thing might be immediately deducted. Check with a pro on that.
Baseboard heat would never be construed as a repair, nor would it get any of the above tax breaks.
A modern heat pump might eliminate the need for a service upgrade. And you known that the owner would kick over it. Hooking up a heat pump is as if it were an airconditioner.