Is it better to have two A/C compressors running or just one?
I would install a split system with a single compressor. A mini split system is very efficient and is designed to supply cooling seperatly where needed the compressor condenser units only run at the speed needed to supply the load on the units I have installed. Electricity is expensive but a 2nd compressor will end up costing significanty more compared to 1 compressor with 2 evaporators (or more) because with 2 you now need 2 disconnects and the extra wiring since they will be in the same location. The only time I would suggest to have 2 compressors is when the home is large and the pressure and suction lines to the evaporators get long in this case it can be cheaper to have units located on opposite sides of the home reducing the line set length. But since the compressors will be located in the same location I would go with a single sized for the evaporators you need.