Lets just say all other things are equal.
		
		
	 
 
Performance first if the second card is noticably different/slower.
 
Cooler size if the performance is similar (generally less noise regardless of power / heat production)
 
Fan type/size (so noise for sure at that point)
 
Though given I perfer dual sloted GPU's with rear vents for the hot air, that might be worth saying Heat first. But then when looking at GPU's, the performance is first.
 
With performance and card design(noise/heat ducting) taken into account, the last two (total heat & power) do not matter to me.