IMO - Whichever is cheaper to get.
A "dual channel" pack of RAM is just 2 single sticks that are certain to be identical enough (they came from the same assembly line right next to each other). Any 2 individual sticks of the same brand/model bought at the same time are most likely from the same line as well. Some like the extra 'warm fuzzy feeling' of getting the 'dual channel' pack. I get whichever is cheaper for the type of RAM I'm looking for.