this is tricky and I don't have numbers
when you drop a seed in a neighbor town you will get a popup sometime later saying something like "seeds were squashed in your neighbors town and give you a list of what you earned (some quantity of fertilizer, corn and spades in multiples of 4 and 8) ( i dont know if/how the speed of the neighbor tapping the creatures affects your numbers.
you you squash a green blob in your town you get corn or fertilizer, the occasional seed, and cash I don't know if you get paid better for squashing earlier but I know that there's a max on the number of creatures you can have running in the your town (ie if you just never tapped on the green creatures, friends couldn't drop new ones (unless the older creatures vanish after a fixed period of time but idk how to test)
frankly the green creatures are easier to spot in my town versus the alien corn but they are harder to catch (they move over all surfaces, disappear on one side of the building reappear on the other) the alien corn in my own town will congregate around where my screen is centered if I just let it set