Triple vs. Dual Channel with 6 sticks of memory
At one point, at wholesale, memory makers were changing designs by the week (well, month, but it felt very quick!), so if you bought in bulk from a supplier, even buying smallish quantities such as 10 sticks, you could get three or four different designs - it was a nightmare as dual channel (back then) didn't always work as some designs were to different (but the majority did work - you just had to find the right combination).
Dual channel kits simply bypassed this as they "guarantee" compatibility.
However, things seem to have settled down, and if you buy from the same company at one time, you usually do get the same sticks.
If I was you, just buy whatever it takes to get the amount of memory you want the cheapest way - so go for the 3 dual channel kits, or even see if you can buy the memory as individual sticks as I have not run in to problems for the past few years.