What is the difference between the stockpile techs in Endless Legend?

Solution 1:

The stockpiles provided by Organized Labor are significantly more efficient in terms of production cost-to-yield.

When I tested on Easy difficulty, I got these results:

          | Cost (Production) | Yield | Cost / Yield (Lower is better)
----------------------------------------------------
Unskilled |   1200            |  175  |   6.9
----------------------------------------------------
Organized |   2500            |  875  |   2.9

As you can see, Organized Labor provides more than double the production/science/food as the corresponding Unskilled Labor-level stockpile per point of production spent on the stockpile. (The numbers adjust somewhat on other difficulties, but the principle will be the same)

It is also worth noting that once you complete researching Organized Labor, all your existing stockpiles will upgrade to the improved yield.