I use multi's as they are convenient. One other thing to keep in mind is that typically 1 channel or multi channel still have the same total wattage. For example, mine the single and the dual are both only capable of the same 700 watts, meaning the dual will have to split that 700 watts.
Normally if powering just flewatt, this is not a big deal, but if trying to drive say a oil heater, forget multi channel as you will not even be able to use any additional channels.