Define eco as used here. Eco is usually some ratio of output to input. If you mean the ratio of peds earned to peds spent, then certainly sweating/fruiting/stoning wins since any money you earn w/o spending any gives you an infinite benefit-to-cost ratio.
You might also consider the ratio of peds earned to time spent, which would vary greatly by skills, equipment, etc. For me right now, both hunting and mining beat out sweating/fruiting for this ratio, while crafting is at the bottom since it's pretty much always negative return.
You might also consider skills gained per ped spent and/or per time spent. Fruiting then would be at the bottom, followed by sweating.