Is there an order among these, in terms of desirability: GEC, Northfield/UN-X-LD, Tidioute, Farm and Field?
Depends on what you are into in terms of "desirability."
When originally planned and designed, they weren't expecting to end up being scarce highly-sought after Veblen goods.
Northfield was the premium brand with extra design elements, so maybe expected to cater to the collector market.
Tidioute (carbon steel) and GEC (stainless) were the "daily carry and use" brands. Same patterns, but generally a bit plainer with the less premium handle materials.
The original 'Red Neck' which became Farm and Field was the "no-nonsense working person's knife" - tool steel, synthetic handles, similar to Case's basic Sod Buster knives.
Originally, the pricing bands were in line with this - Northfield patterns up near $100 or a little over, Tidioute down in the $65 to $85 range, Farm and Field down around $50-60, and GEC stainless, when you could find them, generally similar to Tidioute but the elk stag up there with Northfield.
That was back in the glorious days of the Great Recession and its immediate aftermath, when GEC releases actually made it to dealer inventory, and would sit there for a while waiting to be sold. They had not yet established their reputation for quality to the point where people would be willing to pre-pay for knives that had not yet been produced.
Today is is all about excess demand and limited supply, so the original pricing and market segment targeting no longer applies. But it was originally like I laid out here.