100 Watt Head will work fine, the main thing to worry about with your cabinet is the Ohms Reading in back, most 4X12 cabinets are 16 ohms, the head (as with most) should be able to handle a 16 ohm load (the load of the speakers on the head). 100 Watt heads will have this.
240 Watts, must be a Solid State head. Those typically need more wattage to be louder due to the nature of how they work - to put it in the least words possible.
