Hi. When you open creative mode inventory (and JEI list on the right too), you can see the following arrangement: wooden pipes, cobblestone, iron, diamond, gold (wooden – first, gold – last). Diamond is more expensive than gold (especially in Minecraft 1.10+), so I think more intuitive is that arrangement: wooden pipes, cobblestone, iron, gold, diamond (wooden – first, diamond – last). This should be also applied to extractors, because they are arranged in the same way.